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* [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support
@ 2015-01-11  4:03 David Long
  2015-01-11  4:03 ` [PATCH v4 1/6] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature David Long
                   ` (6 more replies)
  0 siblings, 7 replies; 21+ messages in thread
From: David Long @ 2015-01-11  4:03 UTC (permalink / raw)
  To: linux-arm-kernel, Russell King
  Cc: Sandeepa Prabhu, William Cohen, Steve Capper, Catalin Marinas,
	Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

From: "David A. Long" <dave.long@linaro.org>

This patchset is heavily based on Sandeepa Prabhu's ARM v8 kprobes patches, first
seen in October 2013. This version attempts to address concerns raised by
reviewers and also fixes problems discovered during testing, particularly during
SMP testing.

This patchset adds support for kernel probes(kprobes), jump probes(jprobes)
and return probes(kretprobes) support for ARM64.

The kprobes mechanism makes use of software breakpoint and single stepping
support available in the ARM v8 kernel.

Changes since v2 include:

1) Removal of NOP padding in kprobe XOL slots. Slots are now exactly one
instruction long.
2) Disabling of interrupts during execution in single-step mode.
3) Fixing of numerous problems in instruction simulation code (mostly
thanks to Will Cohen).
4) Support for the HAVE_REGS_AND_STACK_ACCESS_API feature is added, to allow
access to kprobes through debugfs.
5) kprobes is *not* enabled in defconfig.
6) Numerous complaints from checkpatch have been cleaned up, although a couple
remain as removing the function pointer typedefs results in ugly code.

Changes since v3 include:

1) Remove table-driven instruction parsing and replace with an if statement
calling out to old and new instruction test functions in insn.c.
2) I removed the addition of orig_x0 to ptrace.h.
3) Reorder the patches.
4) Replace the previous interrupt disabling (from Will Cohen) with
an improved solution (from Steve Capper).

David A. Long (2):
  arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature
  arm64: Add more test functions to insn.c

Sandeepa Prabhu (4):
  arm64: Kprobes with single stepping support
  arm64: Kprobes instruction simulation support
  arm64: Add kernel return probes support(kretprobes)
  kprobes: Add arm64 case in kprobe example module

 arch/arm64/Kconfig                       |   3 +
 arch/arm64/include/asm/insn.h            |  21 +-
 arch/arm64/include/asm/kprobes.h         |  61 +++
 arch/arm64/include/asm/probes.h          |  50 +++
 arch/arm64/include/asm/ptrace.h          |  32 +-
 arch/arm64/include/uapi/asm/ptrace.h     |  36 ++
 arch/arm64/kernel/Makefile               |   3 +
 arch/arm64/kernel/insn.c                 |  18 +
 arch/arm64/kernel/kprobes-arm64.c        | 161 +++++++
 arch/arm64/kernel/kprobes-arm64.h        |  30 ++
 arch/arm64/kernel/kprobes.c              | 692 +++++++++++++++++++++++++++++++
 arch/arm64/kernel/kprobes.h              |  30 ++
 arch/arm64/kernel/probes-condn-check.c   | 122 ++++++
 arch/arm64/kernel/probes-simulate-insn.c | 174 ++++++++
 arch/arm64/kernel/probes-simulate-insn.h |  33 ++
 arch/arm64/kernel/ptrace.c               | 119 ++++++
 arch/arm64/kernel/vmlinux.lds.S          |   1 +
 samples/kprobes/kprobe_example.c         |   8 +
 18 files changed, 1591 insertions(+), 3 deletions(-)
 create mode 100644 arch/arm64/include/asm/kprobes.h
 create mode 100644 arch/arm64/include/asm/probes.h
 create mode 100644 arch/arm64/kernel/kprobes-arm64.c
 create mode 100644 arch/arm64/kernel/kprobes-arm64.h
 create mode 100644 arch/arm64/kernel/kprobes.c
 create mode 100644 arch/arm64/kernel/kprobes.h
 create mode 100644 arch/arm64/kernel/probes-condn-check.c
 create mode 100644 arch/arm64/kernel/probes-simulate-insn.c
 create mode 100644 arch/arm64/kernel/probes-simulate-insn.h

-- 
1.8.1.2


^ permalink raw reply	[flat|nested] 21+ messages in thread

* [PATCH v4 1/6] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature
  2015-01-11  4:03 [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support David Long
@ 2015-01-11  4:03 ` David Long
  2015-01-12 12:51   ` Steve Capper
  2015-01-11  4:03 ` [PATCH v4 2/6] arm64: Add more test functions to insn.c David Long
                   ` (5 subsequent siblings)
  6 siblings, 1 reply; 21+ messages in thread
From: David Long @ 2015-01-11  4:03 UTC (permalink / raw)
  To: linux-arm-kernel, Russell King
  Cc: Sandeepa Prabhu, William Cohen, Steve Capper, Catalin Marinas,
	Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

From: "David A. Long" <dave.long@linaro.org>

Add HAVE_REGS_AND_STACK_ACCESS_API feature for arm64.

Signed-off-by: David A. Long <dave.long@linaro.org>
---
 arch/arm64/Kconfig                   |   1 +
 arch/arm64/include/asm/ptrace.h      |  29 +++++++++
 arch/arm64/include/uapi/asm/ptrace.h |  36 +++++++++++
 arch/arm64/kernel/ptrace.c           | 119 +++++++++++++++++++++++++++++++++++
 4 files changed, 185 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b1f9a20..12b3fd6 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -64,6 +64,7 @@ config ARM64
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
+	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RCU_TABLE_FREE
 	select HAVE_SYSCALL_TRACEPOINTS
 	select IRQ_DOMAIN
diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index 41ed9e1..3613e49 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -111,6 +111,8 @@ struct pt_regs {
 	u64 syscallno;
 };
 
+#define MAX_REG_OFFSET (sizeof(struct user_pt_regs) - sizeof(u64))
+
 #define arch_has_single_step()	(1)
 
 #ifdef CONFIG_COMPAT
@@ -139,11 +141,38 @@ struct pt_regs {
 #define user_stack_pointer(regs) \
 	(!compat_user_mode(regs) ? (regs)->sp : (regs)->compat_sp)
 
+/**
+ * regs_get_register() - get register value from its offset
+ * @regs:	   pt_regs from which register value is gotten
+ * @offset:    offset number of the register.
+ *
+ * regs_get_register returns the value of a register whose offset from @regs.
+ * The @offset is the offset of the register in struct pt_regs.
+ * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
+ */
+static inline u64 regs_get_register(struct pt_regs *regs,
+					      unsigned int offset)
+{
+	if (unlikely(offset > MAX_REG_OFFSET))
+		return 0;
+	return *(u64 *)((u64)regs + offset);
+}
+
+/* Valid only for Kernel mode traps. */
+static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
+{
+	return regs->ARM_sp;
+}
+
 static inline unsigned long regs_return_value(struct pt_regs *regs)
 {
 	return regs->regs[0];
 }
 
+extern int regs_query_register_offset(const char *name);
+extern unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
+					       unsigned int n);
+
 /*
  * Are the current registers suitable for user mode? (used to maintain
  * security in signal handlers)
diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index 6913643..700d28b 100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -61,6 +61,42 @@
 
 #ifndef __ASSEMBLY__
 
+#define ARM_cpsr	pstate
+#define ARM_pc		pc
+#define ARM_sp		sp
+#define ARM_lr		regs[30]
+#define ARM_fp		regs[29]
+#define ARM_x28		regs[28]
+#define ARM_x27		regs[27]
+#define ARM_x26		regs[26]
+#define ARM_x25		regs[25]
+#define ARM_x24		regs[24]
+#define ARM_x23		regs[23]
+#define ARM_x22		regs[22]
+#define ARM_x21		regs[21]
+#define ARM_x20		regs[20]
+#define ARM_x19		regs[19]
+#define ARM_x18		regs[18]
+#define ARM_ip1		regs[17]
+#define ARM_ip0		regs[16]
+#define ARM_x15		regs[15]
+#define ARM_x14		regs[14]
+#define ARM_x13		regs[13]
+#define ARM_x12		regs[12]
+#define ARM_x11		regs[11]
+#define ARM_x10		regs[10]
+#define ARM_x9		regs[9]
+#define ARM_x8		regs[8]
+#define ARM_x7		regs[7]
+#define ARM_x6		regs[6]
+#define ARM_x5		regs[5]
+#define ARM_x4		regs[4]
+#define ARM_x3		regs[3]
+#define ARM_x2		regs[2]
+#define ARM_x1		regs[1]
+#define ARM_x0		regs[0]
+#define ARM_ORIG_x0	orig_x0
+
 /*
  * User structures for general purpose, floating point and debug registers.
  */
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index d882b83..9115b25 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -48,6 +48,125 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/syscalls.h>
 
+struct pt_regs_offset {
+	const char *name;
+	int offset;
+};
+
+#define REG_OFFSET_NAME(r) \
+	{.name = #r, .offset = offsetof(struct pt_regs, ARM_##r)}
+#define REG_OFFSET_END {.name = NULL, .offset = 0}
+
+static const struct pt_regs_offset regoffset_table[] = {
+	REG_OFFSET_NAME(x0),
+	REG_OFFSET_NAME(x1),
+	REG_OFFSET_NAME(x2),
+	REG_OFFSET_NAME(x3),
+	REG_OFFSET_NAME(x4),
+	REG_OFFSET_NAME(x5),
+	REG_OFFSET_NAME(x6),
+	REG_OFFSET_NAME(x7),
+	REG_OFFSET_NAME(x8),
+	REG_OFFSET_NAME(x9),
+	REG_OFFSET_NAME(x10),
+	REG_OFFSET_NAME(x11),
+	REG_OFFSET_NAME(x12),
+	REG_OFFSET_NAME(x13),
+	REG_OFFSET_NAME(x14),
+	REG_OFFSET_NAME(x15),
+	REG_OFFSET_NAME(ip0),
+	REG_OFFSET_NAME(ip1),
+	REG_OFFSET_NAME(x18),
+	REG_OFFSET_NAME(x19),
+	REG_OFFSET_NAME(x20),
+	REG_OFFSET_NAME(x21),
+	REG_OFFSET_NAME(x22),
+	REG_OFFSET_NAME(x23),
+	REG_OFFSET_NAME(x24),
+	REG_OFFSET_NAME(x25),
+	REG_OFFSET_NAME(x26),
+	REG_OFFSET_NAME(x27),
+	REG_OFFSET_NAME(x28),
+	REG_OFFSET_NAME(fp),
+	REG_OFFSET_NAME(lr),
+/*
+	REG_OFFSET_NAME(ip),
+*/
+	REG_OFFSET_NAME(sp),
+	REG_OFFSET_NAME(pc),
+	REG_OFFSET_NAME(cpsr),
+	REG_OFFSET_NAME(ORIG_x0),
+	REG_OFFSET_END,
+};
+
+/**
+ * regs_query_register_offset() - query register offset from its name
+ * @name:	the name of a register
+ *
+ * regs_query_register_offset() returns the offset of a register in struct
+ * pt_regs from its name. If the name is invalid, this returns -EINVAL;
+ */
+int regs_query_register_offset(const char *name)
+{
+	const struct pt_regs_offset *roff;
+
+	for (roff = regoffset_table; roff->name != NULL; roff++)
+		if (!strcmp(roff->name, name))
+			return roff->offset;
+	return -EINVAL;
+}
+
+/**
+ * regs_query_register_name() - query register name from its offset
+ * @offset:	the offset of a register in struct pt_regs.
+ *
+ * regs_query_register_name() returns the name of a register from its
+ * offset in struct pt_regs. If the @offset is invalid, this returns NULL;
+ */
+const char *regs_query_register_name(unsigned int offset)
+{
+	const struct pt_regs_offset *roff;
+
+	for (roff = regoffset_table; roff->name != NULL; roff++)
+		if (roff->offset == offset)
+			return roff->name;
+	return NULL;
+}
+
+/**
+ * regs_within_kernel_stack() - check the address in the stack
+ * @regs:      pt_regs which contains kernel stack pointer.
+ * @addr:      address which is checked.
+ *
+ * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
+ * If @addr is within the kernel stack, it returns true. If not, returns false.
+ */
+bool regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
+{
+	return ((addr & ~(THREAD_SIZE - 1))  ==
+		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1)));
+}
+
+/**
+ * regs_get_kernel_stack_nth() - get Nth entry of the stack
+ * @regs:	pt_regs which contains kernel stack pointer.
+ * @n:		stack entry number.
+ *
+ * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
+ * is specified by @regs. If the @n th entry is NOT in the kernel stack,
+ * this returns 0.
+ */
+unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
+{
+	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
+
+	addr += n;
+	if (regs_within_kernel_stack(regs, (unsigned long)addr))
+		return *addr;
+	else
+		return 0;
+}
+
 /*
  * TODO: does not yet catch signals sent when the child dies.
  * in exit.c or in signal.c.
-- 
1.8.1.2


^ permalink raw reply	[flat|nested] 21+ messages in thread

* [PATCH v4 2/6] arm64: Add more test functions to insn.c
  2015-01-11  4:03 [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support David Long
  2015-01-11  4:03 ` [PATCH v4 1/6] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature David Long
@ 2015-01-11  4:03 ` David Long
  2015-01-14  9:32   ` Pratyush Anand
  2015-01-11  4:03 ` [PATCH v4 3/6] arm64: Kprobes with single stepping support David Long
                   ` (4 subsequent siblings)
  6 siblings, 1 reply; 21+ messages in thread
From: David Long @ 2015-01-11  4:03 UTC (permalink / raw)
  To: linux-arm-kernel, Russell King
  Cc: Sandeepa Prabhu, William Cohen, Steve Capper, Catalin Marinas,
	Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

From: "David A. Long" <dave.long@linaro.org>

Certain instructions are hard to execute correctly out-of-line (as in
kprobes).  Test functions are added to insn.[hc] to identify these.  The
instructions include any that use PC-relative addressing, change the PC,
or change interrupt masking. For efficiency and simplicity test
functions are also added for small collections of related instructions.

Signed-off-by: David A. Long <dave.long@linaro.org>
---
 arch/arm64/include/asm/insn.h | 21 +++++++++++++++++++--
 arch/arm64/kernel/insn.c      | 18 ++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
index e2ff32a..466afd4 100644
--- a/arch/arm64/include/asm/insn.h
+++ b/arch/arm64/include/asm/insn.h
@@ -223,8 +223,13 @@ static __always_inline bool aarch64_insn_is_##abbr(u32 code) \
 static __always_inline u32 aarch64_insn_get_##abbr##_value(void) \
 { return (val); }
 
+__AARCH64_INSN_FUNCS(adr,	0x9F000000, 0x10000000)
+__AARCH64_INSN_FUNCS(prfm_lit,	0xFF000000, 0xD8000000)
 __AARCH64_INSN_FUNCS(str_reg,	0x3FE0EC00, 0x38206800)
 __AARCH64_INSN_FUNCS(ldr_reg,	0x3FE0EC00, 0x38606800)
+__AARCH64_INSN_FUNCS(ldr_lit,	0xBF000000, 0x18000000)
+__AARCH64_INSN_FUNCS(ldrsw_lit,	0xFF000000, 0x98000000)
+__AARCH64_INSN_FUNCS(exclusive,	0x3F000000, 0x08000000)
 __AARCH64_INSN_FUNCS(stp_post,	0x7FC00000, 0x28800000)
 __AARCH64_INSN_FUNCS(ldp_post,	0x7FC00000, 0x28C00000)
 __AARCH64_INSN_FUNCS(stp_pre,	0x7FC00000, 0x29800000)
@@ -264,9 +269,15 @@ __AARCH64_INSN_FUNCS(ands,	0x7F200000, 0x6A000000)
 __AARCH64_INSN_FUNCS(bics,	0x7F200000, 0x6A200000)
 __AARCH64_INSN_FUNCS(b,		0xFC000000, 0x14000000)
 __AARCH64_INSN_FUNCS(bl,	0xFC000000, 0x94000000)
-__AARCH64_INSN_FUNCS(cbz,	0xFE000000, 0x34000000)
-__AARCH64_INSN_FUNCS(cbnz,	0xFE000000, 0x35000000)
+__AARCH64_INSN_FUNCS(b_bl,	0x7C000000, 0x14000000)
+__AARCH64_INSN_FUNCS(cb,	0x7E000000, 0x34000000)
+__AARCH64_INSN_FUNCS(cbz,	0x7F000000, 0x34000000)
+__AARCH64_INSN_FUNCS(cbnz,	0x7F000000, 0x35000000)
 __AARCH64_INSN_FUNCS(bcond,	0xFF000010, 0x54000000)
+__AARCH64_INSN_FUNCS(tb,	0x7E000000, 0x36000000)
+__AARCH64_INSN_FUNCS(tbz,	0x7F000000, 0x36000000)
+__AARCH64_INSN_FUNCS(tbnz,	0x7F000000, 0x37000000)
+__AARCH64_INSN_FUNCS(b_bl_cb_tb, 0x5C000000, 0x14000000)
 __AARCH64_INSN_FUNCS(svc,	0xFFE0001F, 0xD4000001)
 __AARCH64_INSN_FUNCS(hvc,	0xFFE0001F, 0xD4000002)
 __AARCH64_INSN_FUNCS(smc,	0xFFE0001F, 0xD4000003)
@@ -274,7 +285,11 @@ __AARCH64_INSN_FUNCS(brk,	0xFFE0001F, 0xD4200000)
 __AARCH64_INSN_FUNCS(hint,	0xFFFFF01F, 0xD503201F)
 __AARCH64_INSN_FUNCS(br,	0xFFFFFC1F, 0xD61F0000)
 __AARCH64_INSN_FUNCS(blr,	0xFFFFFC1F, 0xD63F0000)
+__AARCH64_INSN_FUNCS(br_blr,	0xFFDFFC1F, 0xD61F0000)
 __AARCH64_INSN_FUNCS(ret,	0xFFFFFC1F, 0xD65F0000)
+__AARCH64_INSN_FUNCS(msr_imm,	0xFFF8F000, 0xD5004000)
+__AARCH64_INSN_FUNCS(msr_reg,	0xFFF00000, 0xD5100000)
+__AARCH64_INSN_FUNCS(msr_daif,	0xFFFFF0DF, 0xD50340DF)
 
 #undef	__AARCH64_INSN_FUNCS
 
@@ -283,6 +298,8 @@ bool aarch64_insn_is_nop(u32 insn);
 int aarch64_insn_read(void *addr, u32 *insnp);
 int aarch64_insn_write(void *addr, u32 insn);
 enum aarch64_insn_encoding_class aarch64_get_insn_class(u32 insn);
+bool aarch64_insn_uses_literal(u32 insn);
+bool aarch64_insn_is_branch(u32 insn);
 u32 aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
 				  u32 insn, u64 imm);
 u32 aarch64_insn_gen_branch_imm(unsigned long pc, unsigned long addr,
diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
index 7e9327a..8021722 100644
--- a/arch/arm64/kernel/insn.c
+++ b/arch/arm64/kernel/insn.c
@@ -72,6 +72,24 @@ bool __kprobes aarch64_insn_is_nop(u32 insn)
 	}
 }
 
+bool aarch64_insn_uses_literal(u32 insn)
+{
+	/* ldr/ldrsw (literal), prfm */
+
+	return aarch64_insn_is_ldr_lit(insn) ||
+		aarch64_insn_is_ldrsw_lit(insn) ||
+		aarch64_insn_is_prfm_lit(insn);
+}
+
+bool aarch64_insn_is_branch(u32 insn)
+{
+	/* b, bl, cb*, tb*, b.cond, br, blr */
+
+	return aarch64_insn_is_b_bl_cb_tb(insn) ||
+		aarch64_insn_is_br_blr(insn) ||
+		aarch64_insn_is_bcond(insn);
+}
+
 /*
  * In ARMv8-A, A64 instructions have a fixed length of 32 bits and are always
  * little-endian.
-- 
1.8.1.2


^ permalink raw reply	[flat|nested] 21+ messages in thread

* [PATCH v4 3/6] arm64: Kprobes with single stepping support
  2015-01-11  4:03 [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support David Long
  2015-01-11  4:03 ` [PATCH v4 1/6] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature David Long
  2015-01-11  4:03 ` [PATCH v4 2/6] arm64: Add more test functions to insn.c David Long
@ 2015-01-11  4:03 ` David Long
  2015-01-12 13:31   ` Steve Capper
  2015-01-14  9:30   ` Pratyush Anand
  2015-01-11  4:03 ` [PATCH v4 4/6] arm64: Kprobes instruction simulation support David Long
                   ` (3 subsequent siblings)
  6 siblings, 2 replies; 21+ messages in thread
From: David Long @ 2015-01-11  4:03 UTC (permalink / raw)
  To: linux-arm-kernel, Russell King
  Cc: Sandeepa Prabhu, William Cohen, Steve Capper, Catalin Marinas,
	Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>

Add support for basic kernel probes(kprobes) and jump probes
(jprobes) for ARM64.

Kprobes will utilize software breakpoint and single step debug
exceptions supported on ARM v8.

Software breakpoint is placed at the probe address to trap the
kernel execution into kprobe handler.

ARM v8 supports single stepping to be enabled while exception return
(ERET) with next PC in exception return address (ELR_EL1). The
kprobe handler prepares an executable memory slot for out-of-line
execution with a copy of the original instruction being probed, and
enables single stepping from the instruction slot. With this scheme,
the instruction is executed with the exact same register context
'except PC' that points to instruction slot.

Debug mask(PSTATE.D) is enabled only when single stepping a recursive
kprobe, e.g.: during kprobes reenter so that probed instruction can be
single stepped within the kprobe handler -exception- context.
The recursion depth of kprobe is always 2, i.e. upon probe re-entry,
any further re-entry is prevented by not calling handlers and the case
counted as a missed kprobe).

Single stepping from slot has a drawback on PC-relative accesses
like branching and symbolic literals access as offset from new PC
(slot address) may not be ensured to fit in immediate value of
opcode. Such instructions needs simulation, so reject
probing such instructions.

Instructions generating exceptions or cpu mode change are rejected,
and not allowed to insert probe for these instructions.

Instructions using Exclusive Monitor are rejected too.

System instructions are mostly enabled for stepping, except MSR
immediate that updates "daif" flags in PSTATE, which are not safe
for probing.

Changes since v3:
from David Long:
1) Removed unnecessary addtion of NOP after out-of-line instruction.
2) Replaced table-driven instruction parsing with calls to external
   test functions.
from Steve Capper:
3) Disable local irq while executing out of line instruction.

Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
Signed-off-by: Steve Capper <steve.capper@linaro.org>
Signed-off-by: David A. Long <dave.long@linaro.org>
---
 arch/arm64/Kconfig                |   1 +
 arch/arm64/include/asm/kprobes.h  |  60 +++++
 arch/arm64/include/asm/probes.h   |  50 ++++
 arch/arm64/include/asm/ptrace.h   |   3 +-
 arch/arm64/kernel/Makefile        |   1 +
 arch/arm64/kernel/kprobes-arm64.c |  65 +++++
 arch/arm64/kernel/kprobes-arm64.h |  28 ++
 arch/arm64/kernel/kprobes.c       | 551 ++++++++++++++++++++++++++++++++++++++
 arch/arm64/kernel/kprobes.h       |  30 +++
 arch/arm64/kernel/vmlinux.lds.S   |   1 +
 10 files changed, 789 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm64/include/asm/kprobes.h
 create mode 100644 arch/arm64/include/asm/probes.h
 create mode 100644 arch/arm64/kernel/kprobes-arm64.c
 create mode 100644 arch/arm64/kernel/kprobes-arm64.h
 create mode 100644 arch/arm64/kernel/kprobes.c
 create mode 100644 arch/arm64/kernel/kprobes.h

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 12b3fd6..b3f61ba 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -67,6 +67,7 @@ config ARM64
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RCU_TABLE_FREE
 	select HAVE_SYSCALL_TRACEPOINTS
+	select HAVE_KPROBES if !XIP_KERNEL
 	select IRQ_DOMAIN
 	select MODULES_USE_ELF_RELA
 	select NO_BOOTMEM
diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
new file mode 100644
index 0000000..b35d3b9
--- /dev/null
+++ b/arch/arm64/include/asm/kprobes.h
@@ -0,0 +1,60 @@
+/*
+ * arch/arm64/include/asm/kprobes.h
+ *
+ * Copyright (C) 2013 Linaro Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#ifndef _ARM_KPROBES_H
+#define _ARM_KPROBES_H
+
+#include <linux/types.h>
+#include <linux/ptrace.h>
+#include <linux/percpu.h>
+
+#define __ARCH_WANT_KPROBES_INSN_SLOT
+#define MAX_INSN_SIZE			1
+#define MAX_STACK_SIZE			128
+
+#define flush_insn_slot(p)		do { } while (0)
+#define kretprobe_blacklist_size	0
+
+#include <asm/probes.h>
+
+struct prev_kprobe {
+	struct kprobe *kp;
+	unsigned int status;
+};
+
+/* Single step context for kprobe */
+struct kprobe_step_ctx {
+#define KPROBES_STEP_NONE	0x0
+#define KPROBES_STEP_PENDING	0x1
+	unsigned long ss_status;
+	unsigned long match_addr;
+};
+
+/* per-cpu kprobe control block */
+struct kprobe_ctlblk {
+	unsigned int kprobe_status;
+	unsigned long saved_irqflag;
+	struct prev_kprobe prev_kprobe;
+	struct kprobe_step_ctx ss_ctx;
+	struct pt_regs jprobe_saved_regs;
+	char jprobes_stack[MAX_STACK_SIZE];
+};
+
+void arch_remove_kprobe(struct kprobe *);
+int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
+int kprobe_exceptions_notify(struct notifier_block *self,
+			     unsigned long val, void *data);
+
+#endif /* _ARM_KPROBES_H */
diff --git a/arch/arm64/include/asm/probes.h b/arch/arm64/include/asm/probes.h
new file mode 100644
index 0000000..9dba74d
--- /dev/null
+++ b/arch/arm64/include/asm/probes.h
@@ -0,0 +1,50 @@
+/*
+ * arch/arm64/include/asm/probes.h
+ *
+ * Copyright (C) 2013 Linaro Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#ifndef _ARM_PROBES_H
+#define _ARM_PROBES_H
+
+struct kprobe;
+struct arch_specific_insn;
+
+typedef u32 kprobe_opcode_t;
+typedef unsigned long (kprobes_pstate_check_t)(unsigned long);
+typedef unsigned long
+(kprobes_condition_check_t)(struct kprobe *p, struct pt_regs *);
+typedef void
+(kprobes_prepare_t)(struct kprobe *, struct arch_specific_insn *);
+typedef void (kprobes_handler_t) (u32 opcode, long addr, struct pt_regs *);
+
+enum pc_restore_type {
+	NO_RESTORE,
+	RESTORE_PC,
+};
+
+struct kprobe_pc_restore {
+	enum pc_restore_type type;
+	unsigned long addr;
+};
+
+/* architecture specific copy of original instruction */
+struct arch_specific_insn {
+	kprobe_opcode_t *insn;
+	kprobes_pstate_check_t *pstate_cc;
+	kprobes_condition_check_t *check_condn;
+	kprobes_prepare_t *prepare;
+	kprobes_handler_t *handler;
+	/* restore address after step xol */
+	struct kprobe_pc_restore restore;
+};
+
+#endif
diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index 3613e49..e436b49 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -203,7 +203,8 @@ static inline int valid_user_regs(struct user_pt_regs *regs)
 	return 0;
 }
 
-#define instruction_pointer(regs)	((unsigned long)(regs)->pc)
+#define instruction_pointer(regs)	((regs)->pc)
+#define stack_pointer(regs)		((regs)->sp)
 
 #ifdef CONFIG_SMP
 extern unsigned long profile_pc(struct pt_regs *regs);
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index eaa77ed..6ca9fc0 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -31,6 +31,7 @@ arm64-obj-$(CONFIG_ARM64_CPU_SUSPEND)	+= sleep.o suspend.o
 arm64-obj-$(CONFIG_CPU_IDLE)		+= cpuidle.o
 arm64-obj-$(CONFIG_JUMP_LABEL)		+= jump_label.o
 arm64-obj-$(CONFIG_KGDB)		+= kgdb.o
+arm64-obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes-arm64.o
 arm64-obj-$(CONFIG_EFI)			+= efi.o efi-stub.o efi-entry.o
 arm64-obj-$(CONFIG_PCI)			+= pci.o
 arm64-obj-$(CONFIG_ARMV8_DEPRECATED)	+= armv8_deprecated.o
diff --git a/arch/arm64/kernel/kprobes-arm64.c b/arch/arm64/kernel/kprobes-arm64.c
new file mode 100644
index 0000000..a698bd3
--- /dev/null
+++ b/arch/arm64/kernel/kprobes-arm64.c
@@ -0,0 +1,65 @@
+/*
+ * arch/arm64/kernel/kprobes-arm64.c
+ *
+ * Copyright (C) 2013 Linaro Limited.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+#include <linux/module.h>
+#include <asm/kprobes.h>
+#include <asm/insn.h>
+
+#include "kprobes-arm64.h"
+
+static bool aarch64_insn_is_steppable(u32 insn)
+{
+	if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
+		if (aarch64_insn_is_branch(insn))
+			return false;
+
+		/* modification of daif creates issues */
+		if (aarch64_insn_is_msr_daif(insn))
+			return false;
+
+		if (aarch64_insn_is_hint(insn))
+			return aarch64_insn_is_nop(insn);
+
+		return true;
+	}
+
+	if (aarch64_insn_uses_literal(insn))
+		return false;
+
+	if (aarch64_insn_is_exclusive(insn))
+		return false;
+
+	return true;
+}
+
+/* Return:
+ *   INSN_REJECTED     If instruction is one not allowed to kprobe,
+ *   INSN_GOOD         If instruction is supported and uses instruction slot,
+ *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
+ */
+enum kprobe_insn __kprobes
+arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
+{
+	/*
+	 * Instructions reading or modifying the PC won't work from the XOL
+	 * slot.
+	 */
+	if (aarch64_insn_is_steppable(insn))
+		return INSN_GOOD;
+	else
+		return INSN_REJECTED;
+}
diff --git a/arch/arm64/kernel/kprobes-arm64.h b/arch/arm64/kernel/kprobes-arm64.h
new file mode 100644
index 0000000..87e7891
--- /dev/null
+++ b/arch/arm64/kernel/kprobes-arm64.h
@@ -0,0 +1,28 @@
+/*
+ * arch/arm64/kernel/kprobes-arm64.h
+ *
+ * Copyright (C) 2013 Linaro Limited.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#ifndef _ARM_KERNEL_KPROBES_ARM64_H
+#define _ARM_KERNEL_KPROBES_ARM64_H
+
+enum kprobe_insn {
+	INSN_REJECTED,
+	INSN_GOOD_NO_SLOT,
+	INSN_GOOD,
+};
+
+enum kprobe_insn __kprobes
+arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi);
+
+#endif /* _ARM_KERNEL_KPROBES_ARM64_H */
diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
new file mode 100644
index 0000000..65e22d8
--- /dev/null
+++ b/arch/arm64/kernel/kprobes.c
@@ -0,0 +1,551 @@
+/*
+ * arch/arm64/kernel/kprobes.c
+ *
+ * Kprobes support for ARM64
+ *
+ * Copyright (C) 2013 Linaro Limited.
+ * Author: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/stop_machine.h>
+#include <linux/stringify.h>
+#include <asm/traps.h>
+#include <asm/ptrace.h>
+#include <asm/cacheflush.h>
+#include <asm/debug-monitors.h>
+#include <asm/system_misc.h>
+#include <asm/insn.h>
+
+#include "kprobes.h"
+#include "kprobes-arm64.h"
+
+#define MIN_STACK_SIZE(addr)	min((unsigned long)MAX_STACK_SIZE,	\
+	(unsigned long)current_thread_info() + THREAD_START_SP - (addr))
+
+DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
+DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
+
+static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
+{
+	/* prepare insn slot */
+	p->ainsn.insn[0] = p->opcode;
+
+	flush_icache_range((uintptr_t) (p->ainsn.insn),
+			   (uintptr_t) (p->ainsn.insn) + MAX_INSN_SIZE);
+
+	/*
+	 * Needs restoring of return address after stepping xol.
+	 */
+	p->ainsn.restore.addr = (unsigned long) p->addr +
+	  sizeof(kprobe_opcode_t);
+	p->ainsn.restore.type = RESTORE_PC;
+}
+
+int __kprobes arch_prepare_kprobe(struct kprobe *p)
+{
+	kprobe_opcode_t insn;
+	unsigned long probe_addr = (unsigned long)p->addr;
+
+	/* copy instruction */
+	insn = *p->addr;
+	p->opcode = insn;
+
+	if (in_exception_text(probe_addr))
+		return -EINVAL;
+
+	/* decode instruction */
+	switch (arm_kprobe_decode_insn(insn, &p->ainsn)) {
+	case INSN_REJECTED:	/* insn not supported */
+		return -EINVAL;
+
+	case INSN_GOOD_NO_SLOT:	/* insn need simulation */
+		return -EINVAL;
+
+	case INSN_GOOD:	/* instruction uses slot */
+		p->ainsn.insn = get_insn_slot();
+		if (!p->ainsn.insn)
+			return -ENOMEM;
+		break;
+	};
+
+	/* prepare the instruction */
+	arch_prepare_ss_slot(p);
+
+	return 0;
+}
+
+static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
+{
+	void *addrs[1];
+	u32 insns[1];
+
+	addrs[0] = (void *)addr;
+	insns[0] = (u32)opcode;
+
+	return aarch64_insn_patch_text_sync(addrs, insns, 1);
+}
+
+/* arm kprobe: install breakpoint in text */
+void __kprobes arch_arm_kprobe(struct kprobe *p)
+{
+	patch_text(p->addr, BRK64_OPCODE_KPROBES);
+}
+
+/* disarm kprobe: remove breakpoint from text */
+void __kprobes arch_disarm_kprobe(struct kprobe *p)
+{
+	patch_text(p->addr, p->opcode);
+}
+
+void __kprobes arch_remove_kprobe(struct kprobe *p)
+{
+	if (p->ainsn.insn) {
+		free_insn_slot(p->ainsn.insn, 0);
+		p->ainsn.insn = NULL;
+	}
+}
+
+static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	kcb->prev_kprobe.kp = kprobe_running();
+	kcb->prev_kprobe.status = kcb->kprobe_status;
+}
+
+static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
+{
+	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
+	kcb->kprobe_status = kcb->prev_kprobe.status;
+}
+
+static void __kprobes set_current_kprobe(struct kprobe *p)
+{
+	__this_cpu_write(current_kprobe, p);
+}
+
+/*
+ * Debug flag (D-flag) is disabled upon exception entry.
+ * Kprobes need to unmask D-flag -ONLY- in case of recursive
+ * probe i.e. when probe hit from kprobe handler context upon
+ * executing the pre/post handlers. In this case we return with
+ * D-flag unmasked so that single-stepping can be carried-out.
+ *
+ * Keep D-flag masked in all other cases.
+ */
+static void __kprobes
+spsr_set_debug_flag(struct pt_regs *regs, int mask)
+{
+	unsigned long spsr = regs->pstate;
+
+	if (mask)
+		spsr |= PSR_D_BIT;
+	else
+		spsr &= ~PSR_D_BIT;
+
+	regs->pstate = spsr;
+}
+
+/*
+ * Interrupt needs to be disabled for the duration from probe hitting
+ * breakpoint exception until kprobe is processed completely.
+ * Without disabling interrupt on local CPU, there is a chance of
+ * interrupt occurrence in the period of exception return and  start of
+ * out-of-line single-step, that result in wrongly single stepping
+ * the interrupt handler.
+ */
+static void __kprobes kprobes_save_local_irqflag(struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	kcb->saved_irqflag = regs->pstate;
+	regs->pstate |= PSR_I_BIT;
+}
+
+static void __kprobes kprobes_restore_local_irqflag(struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	if (kcb->saved_irqflag & PSR_I_BIT)
+		regs->pstate |= PSR_I_BIT;
+	else
+		regs->pstate &= ~PSR_I_BIT;
+}
+
+static void __kprobes
+set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
+{
+	kcb->ss_ctx.ss_status = KPROBES_STEP_PENDING;
+	kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
+}
+
+static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
+{
+	kcb->ss_ctx.ss_status = KPROBES_STEP_NONE;
+	kcb->ss_ctx.match_addr = 0;
+}
+
+static void __kprobes
+skip_singlestep_missed(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
+{
+	/* set return addr to next pc to continue */
+	instruction_pointer(regs) += sizeof(kprobe_opcode_t);
+}
+
+static void __kprobes setup_singlestep(struct kprobe *p,
+				       struct pt_regs *regs,
+				       struct kprobe_ctlblk *kcb, int reenter)
+{
+	unsigned long slot;
+
+	if (reenter) {
+		save_previous_kprobe(kcb);
+		set_current_kprobe(p);
+		kcb->kprobe_status = KPROBE_REENTER;
+	} else {
+		kcb->kprobe_status = KPROBE_HIT_SS;
+	}
+
+	if (p->ainsn.insn) {
+		/* prepare for single stepping */
+		slot = (unsigned long)p->ainsn.insn;
+
+		set_ss_context(kcb, slot);	/* mark pending ss */
+
+		if (kcb->kprobe_status == KPROBE_REENTER)
+			spsr_set_debug_flag(regs, 0);
+
+		/* IRQs and single stepping do not mix well. */
+		kprobes_save_local_irqflag(regs);
+		kernel_enable_single_step(regs);
+		instruction_pointer(regs) = slot;
+	} else	{
+		BUG();
+	}
+}
+
+static int __kprobes reenter_kprobe(struct kprobe *p,
+				    struct pt_regs *regs,
+				    struct kprobe_ctlblk *kcb)
+{
+	switch (kcb->kprobe_status) {
+	case KPROBE_HIT_SSDONE:
+	case KPROBE_HIT_ACTIVE:
+		if (!p->ainsn.check_condn || p->ainsn.check_condn(p, regs)) {
+			kprobes_inc_nmissed_count(p);
+			setup_singlestep(p, regs, kcb, 1);
+		} else	{
+			/* condition check failed, skip stepping */
+			skip_singlestep_missed(kcb, regs);
+		}
+		break;
+	case KPROBE_HIT_SS:
+		pr_warn("Unrecoverable kprobe detected at %p.\n", p->addr);
+		dump_kprobe(p);
+		BUG();
+		break;
+	default:
+		WARN_ON(1);
+		return 0;
+	}
+
+	return 1;
+}
+
+static void __kprobes
+post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
+{
+	struct kprobe *cur = kprobe_running();
+
+	if (!cur)
+		return;
+
+	/* return addr restore if non-branching insn */
+	if (cur->ainsn.restore.type == RESTORE_PC) {
+		instruction_pointer(regs) = cur->ainsn.restore.addr;
+		if (!instruction_pointer(regs))
+			BUG();
+	}
+
+	/* restore back original saved kprobe variables and continue */
+	if (kcb->kprobe_status == KPROBE_REENTER) {
+		restore_previous_kprobe(kcb);
+		return;
+	}
+	/* call post handler */
+	kcb->kprobe_status = KPROBE_HIT_SSDONE;
+	if (cur->post_handler)	{
+		/* post_handler can hit breakpoint and single step
+		 * again, so we enable D-flag for recursive exception.
+		 */
+		cur->post_handler(cur, regs, 0);
+	}
+
+	reset_current_kprobe();
+}
+
+int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
+{
+	struct kprobe *cur = kprobe_running();
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	switch (kcb->kprobe_status) {
+	case KPROBE_HIT_SS:
+	case KPROBE_REENTER:
+		/*
+		 * We are here because the instruction being single
+		 * stepped caused a page fault. We reset the current
+		 * kprobe and the ip points back to the probe address
+		 * and allow the page fault handler to continue as a
+		 * normal page fault.
+		 */
+		instruction_pointer(regs) = (unsigned long)cur->addr;
+		if (!instruction_pointer(regs))
+			BUG();
+		if (kcb->kprobe_status == KPROBE_REENTER)
+			restore_previous_kprobe(kcb);
+		else
+			reset_current_kprobe();
+
+		break;
+	case KPROBE_HIT_ACTIVE:
+	case KPROBE_HIT_SSDONE:
+		/*
+		 * We increment the nmissed count for accounting,
+		 * we can also use npre/npostfault count for accounting
+		 * these specific fault cases.
+		 */
+		kprobes_inc_nmissed_count(cur);
+
+		/*
+		 * We come here because instructions in the pre/post
+		 * handler caused the page_fault, this could happen
+		 * if handler tries to access user space by
+		 * copy_from_user(), get_user() etc. Let the
+		 * user-specified handler try to fix it first.
+		 */
+		if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
+			return 1;
+
+		/*
+		 * In case the user-specified fault handler returned
+		 * zero, try to fix up.
+		 */
+		if (fixup_exception(regs))
+			return 1;
+
+		break;
+	}
+	return 0;
+}
+
+int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
+				       unsigned long val, void *data)
+{
+	return NOTIFY_DONE;
+}
+
+void __kprobes kprobe_handler(struct pt_regs *regs)
+{
+	struct kprobe *p, *cur;
+	struct kprobe_ctlblk *kcb;
+	unsigned long addr = instruction_pointer(regs);
+
+	kcb = get_kprobe_ctlblk();
+	cur = kprobe_running();
+
+	p = get_kprobe((kprobe_opcode_t *) addr);
+
+	if (p) {
+		if (cur) {
+			if (reenter_kprobe(p, regs, kcb))
+				return;
+		} else if (!p->ainsn.check_condn ||
+			   p->ainsn.check_condn(p, regs)) {
+			/* Probe hit and conditional execution check ok. */
+			set_current_kprobe(p);
+			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+
+			/*
+			 * If we have no pre-handler or it returned 0, we
+			 * continue with normal processing.  If we have a
+			 * pre-handler and it returned non-zero, it prepped
+			 * for calling the break_handler below on re-entry,
+			 * so get out doing nothing more here.
+			 *
+			 * pre_handler can hit a breakpoint and can step thru
+			 * before return, keep PSTATE D-flag enabled until
+			 * pre_handler return back.
+			 */
+			if (!p->pre_handler || !p->pre_handler(p, regs)) {
+				kcb->kprobe_status = KPROBE_HIT_SS;
+				setup_singlestep(p, regs, kcb, 0);
+				return;
+			}
+		} else {
+			/*
+			 * Breakpoint hit but conditional check failed,
+			 * so just skip the instruction (NOP behaviour)
+			 */
+			skip_singlestep_missed(kcb, regs);
+			return;
+		}
+	} else if (*(kprobe_opcode_t *) addr != BRK64_OPCODE_KPROBES) {
+		/*
+		 * The breakpoint instruction was removed right
+		 * after we hit it.  Another cpu has removed
+		 * either a probepoint or a debugger breakpoint
+		 * at this address.  In either case, no further
+		 * handling of this interrupt is appropriate.
+		 * Return back to original instruction, and continue.
+		 */
+		return;
+	} else if (cur) {
+		/* We probably hit a jprobe.  Call its break handler. */
+		if (cur->break_handler && cur->break_handler(cur, regs)) {
+			kcb->kprobe_status = KPROBE_HIT_SS;
+			setup_singlestep(cur, regs, kcb, 0);
+			return;
+		}
+	} else {
+		/* breakpoint is removed, now in a race
+		 * Return back to original instruction & continue.
+		 */
+	}
+}
+
+static int __kprobes
+kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
+{
+	if ((kcb->ss_ctx.ss_status == KPROBES_STEP_PENDING)
+	    && (kcb->ss_ctx.match_addr == addr)) {
+		clear_ss_context(kcb);	/* clear pending ss */
+		return DBG_HOOK_HANDLED;
+	}
+	/* not ours, kprobes should ignore it */
+	return DBG_HOOK_ERROR;
+}
+
+static int __kprobes
+kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	int retval;
+
+	/* return error if this is not our step */
+	retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
+
+	if (retval == DBG_HOOK_HANDLED) {
+		kprobes_restore_local_irqflag(regs);
+		kernel_disable_single_step();
+
+		if (kcb->kprobe_status == KPROBE_REENTER)
+			spsr_set_debug_flag(regs, 1);
+
+		post_kprobe_handler(kcb, regs);
+	}
+
+	return retval;
+}
+
+static int __kprobes
+kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
+{
+	kprobe_handler(regs);
+	return DBG_HOOK_HANDLED;
+}
+
+int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	struct jprobe *jp = container_of(p, struct jprobe, kp);
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	long stack_ptr = stack_pointer(regs);
+
+	kcb->jprobe_saved_regs = *regs;
+	memcpy(kcb->jprobes_stack, (void *)stack_ptr,
+	       MIN_STACK_SIZE(stack_ptr));
+
+	instruction_pointer(regs) = (long)jp->entry;
+	preempt_disable();
+	return 1;
+}
+
+void __kprobes jprobe_return(void)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	/*
+	 * Jprobe handler return by entering break exception,
+	 * encoded same as kprobe, but with following conditions
+	 * -a magic number in x0 to identify from rest of other kprobes.
+	 * -restore stack addr to original saved pt_regs
+	 */
+	asm volatile ("ldr x0, [%0]\n\t"
+		      "mov sp, x0\n\t"
+		      "ldr x0, =" __stringify(JPROBES_MAGIC_NUM) "\n\t"
+		      "BRK %1\n\t"
+		      "NOP\n\t"
+		      :
+		      : "r"(&kcb->jprobe_saved_regs.sp),
+		      "I"(BRK64_ESR_KPROBES)
+		      : "memory");
+}
+
+int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	long stack_addr = kcb->jprobe_saved_regs.sp;
+	long orig_sp = stack_pointer(regs);
+	struct jprobe *jp = container_of(p, struct jprobe, kp);
+
+	if (regs->regs[0] == JPROBES_MAGIC_NUM) {
+		if (orig_sp != stack_addr) {
+			struct pt_regs *saved_regs =
+			    (struct pt_regs *)kcb->jprobe_saved_regs.sp;
+			pr_err("current sp %lx does not match saved sp %lx\n",
+			       orig_sp, stack_addr);
+			pr_err("Saved registers for jprobe %p\n", jp);
+			show_regs(saved_regs);
+			pr_err("Current registers\n");
+			show_regs(regs);
+			BUG();
+		}
+		*regs = kcb->jprobe_saved_regs;
+		memcpy((void *)stack_addr, kcb->jprobes_stack,
+		       MIN_STACK_SIZE(stack_addr));
+		preempt_enable_no_resched();
+		return 1;
+	}
+	return 0;
+}
+
+/* Break Handler hook */
+static struct break_hook kprobes_break_hook = {
+	.esr_mask = BRK64_ESR_MASK,
+	.esr_val = BRK64_ESR_KPROBES,
+	.fn = kprobe_breakpoint_handler,
+};
+
+/* Single Step handler hook */
+static struct step_hook kprobes_step_hook = {
+	.fn = kprobe_single_step_handler,
+};
+
+int __init arch_init_kprobes(void)
+{
+	register_break_hook(&kprobes_break_hook);
+	register_step_hook(&kprobes_step_hook);
+
+	return 0;
+}
diff --git a/arch/arm64/kernel/kprobes.h b/arch/arm64/kernel/kprobes.h
new file mode 100644
index 0000000..93c54b4
--- /dev/null
+++ b/arch/arm64/kernel/kprobes.h
@@ -0,0 +1,30 @@
+/*
+ * arch/arm64/kernel/kprobes.h
+ *
+ * Copyright (C) 2013 Linaro Limited.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#ifndef _ARM_KERNEL_KPROBES_H
+#define _ARM_KERNEL_KPROBES_H
+
+/* BRK opcodes with ESR encoding  */
+#define BRK64_ESR_MASK		0xFFFF
+#define BRK64_ESR_KPROBES	0x0004
+#define BRK64_OPCODE_KPROBES	0xD4200080	/* "brk 0x4" */
+#define ARCH64_NOP_OPCODE	0xD503201F
+
+#define JPROBES_MAGIC_NUM	0xa5a5a5a5a5a5a5a5
+
+/* Move this out to appropriate header file */
+int fixup_exception(struct pt_regs *regs);
+
+#endif /* _ARM_KERNEL_KPROBES_H */
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 9965ec8..5402a98 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -80,6 +80,7 @@ SECTIONS
 			TEXT_TEXT
 			SCHED_TEXT
 			LOCK_TEXT
+			KPROBES_TEXT
 			HYPERVISOR_TEXT
 			*(.fixup)
 			*(.gnu.warning)
-- 
1.8.1.2


^ permalink raw reply	[flat|nested] 21+ messages in thread

* [PATCH v4 4/6] arm64: Kprobes instruction simulation support
  2015-01-11  4:03 [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support David Long
                   ` (2 preceding siblings ...)
  2015-01-11  4:03 ` [PATCH v4 3/6] arm64: Kprobes with single stepping support David Long
@ 2015-01-11  4:03 ` David Long
  2015-01-14  9:32   ` Pratyush Anand
  2015-01-11  4:03 ` [PATCH v4 5/6] arm64: Add kernel return probes support(kretprobes) David Long
                   ` (2 subsequent siblings)
  6 siblings, 1 reply; 21+ messages in thread
From: David Long @ 2015-01-11  4:03 UTC (permalink / raw)
  To: linux-arm-kernel, Russell King
  Cc: Sandeepa Prabhu, William Cohen, Steve Capper, Catalin Marinas,
	Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>

Add support for AArch64 instruction simulation in kprobes.

Kprobes needs simulation of instructions that cannot be stepped
from different memory location, e.g.: those instructions
that uses PC-relative addressing. In simulation, the behaviour
of the instruction is implemented using a copy of pt_regs.

Following instruction catagories are simulated:
 - All branching instructions(conditional, register, and immediate)
 - Literal access instructions(load-literal, adr/adrp)

Conditional execution is limited to branching instructions in
ARM v8. If conditions at PSTATE do not match the condition fields
of opcode, the instruction is effectively NOP. Kprobes considers
this case as 'miss'.
changes since v3:
from David A. Long:
1) Fix incorrect simulate_ldrsw_literal() semantics.
2) Use instruction test functions instead of private parse table.
from Will Cohen:
3) Remove PC adjustments when simulating an instruction.
4) Fix displacement calculations.

Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
Signed-off-by: William Cohen <wcohen@redhat.com>
Signed-off-by: David A. Long <dave.long@linaro.org>
---
 arch/arm64/kernel/Makefile               |   4 +-
 arch/arm64/kernel/kprobes-arm64.c        |  96 +++++++++++++++++
 arch/arm64/kernel/kprobes-arm64.h        |   2 +
 arch/arm64/kernel/kprobes.c              |  35 ++++++-
 arch/arm64/kernel/probes-condn-check.c   | 122 ++++++++++++++++++++++
 arch/arm64/kernel/probes-simulate-insn.c | 174 +++++++++++++++++++++++++++++++
 arch/arm64/kernel/probes-simulate-insn.h |  33 ++++++
 7 files changed, 462 insertions(+), 4 deletions(-)
 create mode 100644 arch/arm64/kernel/probes-condn-check.c
 create mode 100644 arch/arm64/kernel/probes-simulate-insn.c
 create mode 100644 arch/arm64/kernel/probes-simulate-insn.h

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 6ca9fc0..6e4dcde 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -31,7 +31,9 @@ arm64-obj-$(CONFIG_ARM64_CPU_SUSPEND)	+= sleep.o suspend.o
 arm64-obj-$(CONFIG_CPU_IDLE)		+= cpuidle.o
 arm64-obj-$(CONFIG_JUMP_LABEL)		+= jump_label.o
 arm64-obj-$(CONFIG_KGDB)		+= kgdb.o
-arm64-obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes-arm64.o
+arm64-obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes-arm64.o		\
+					   probes-simulate-insn.o		\
+					   probes-condn-check.o
 arm64-obj-$(CONFIG_EFI)			+= efi.o efi-stub.o efi-entry.o
 arm64-obj-$(CONFIG_PCI)			+= pci.o
 arm64-obj-$(CONFIG_ARMV8_DEPRECATED)	+= armv8_deprecated.o
diff --git a/arch/arm64/kernel/kprobes-arm64.c b/arch/arm64/kernel/kprobes-arm64.c
index a698bd3..531d14a 100644
--- a/arch/arm64/kernel/kprobes-arm64.c
+++ b/arch/arm64/kernel/kprobes-arm64.c
@@ -20,6 +20,76 @@
 #include <asm/insn.h>
 
 #include "kprobes-arm64.h"
+#include "probes-simulate-insn.h"
+
+/*
+ * condition check functions for kprobes simulation
+ */
+static unsigned long __kprobes
+__check_pstate(struct kprobe *p, struct pt_regs *regs)
+{
+	struct arch_specific_insn *asi = &p->ainsn;
+	unsigned long pstate = regs->pstate & 0xffffffff;
+
+	return asi->pstate_cc(pstate);
+}
+
+static unsigned long __kprobes
+__check_cbz(struct kprobe *p, struct pt_regs *regs)
+{
+	return check_cbz((u32)p->opcode, regs);
+}
+
+static unsigned long __kprobes
+__check_cbnz(struct kprobe *p, struct pt_regs *regs)
+{
+	return check_cbnz((u32)p->opcode, regs);
+}
+
+static unsigned long __kprobes
+__check_tbz(struct kprobe *p, struct pt_regs *regs)
+{
+	return check_tbz((u32)p->opcode, regs);
+}
+
+static unsigned long __kprobes
+__check_tbnz(struct kprobe *p, struct pt_regs *regs)
+{
+	return check_tbnz((u32)p->opcode, regs);
+}
+
+/*
+ * prepare functions for instruction simulation
+ */
+static void __kprobes
+prepare_none(struct kprobe *p, struct arch_specific_insn *asi)
+{
+}
+
+static void __kprobes
+prepare_bcond(struct kprobe *p, struct arch_specific_insn *asi)
+{
+	kprobe_opcode_t insn = p->opcode;
+
+	asi->check_condn = __check_pstate;
+	asi->pstate_cc = kprobe_condition_checks[insn & 0xf];
+}
+
+static void __kprobes
+prepare_cbz_cbnz(struct kprobe *p, struct arch_specific_insn *asi)
+{
+	kprobe_opcode_t insn = p->opcode;
+
+	asi->check_condn = (insn & (1 << 24)) ? __check_cbnz : __check_cbz;
+}
+
+static void __kprobes
+prepare_tbz_tbnz(struct kprobe *p, struct arch_specific_insn *asi)
+{
+	kprobe_opcode_t insn = p->opcode;
+
+	asi->check_condn = (insn & (1 << 24)) ? __check_tbnz : __check_tbz;
+}
 
 static bool aarch64_insn_is_steppable(u32 insn)
 {
@@ -60,6 +130,32 @@ arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 	 */
 	if (aarch64_insn_is_steppable(insn))
 		return INSN_GOOD;
+
+	asi->prepare = prepare_none;
+
+	if (aarch64_insn_is_bcond(insn)) {
+		asi->prepare = prepare_bcond;
+		asi->handler = simulate_b_cond;
+	} else if (aarch64_insn_is_cb(insn)) {
+		asi->prepare = prepare_cbz_cbnz;
+		asi->handler = simulate_cbz_cbnz;
+	} else if (aarch64_insn_is_tb(insn)) {
+		asi->prepare = prepare_tbz_tbnz;
+		asi->handler = simulate_tbz_tbnz;
+	} else if (aarch64_insn_is_adr(insn))
+		asi->handler = simulate_adr_adrp;
+	else if (aarch64_insn_is_b_bl(insn))
+		asi->handler = simulate_b_bl;
+	else if (aarch64_insn_is_ldr_lit(insn))
+		asi->handler = simulate_ldr_literal;
+	else if (aarch64_insn_is_ldrsw_lit(insn))
+		asi->handler = simulate_ldrsw_literal;
 	else
+		/*
+		 * Instruction cannot be stepped out-of-line and we don't
+		 * (yet) simulate it.
+		 */
 		return INSN_REJECTED;
+
+	return INSN_GOOD_NO_SLOT;
 }
diff --git a/arch/arm64/kernel/kprobes-arm64.h b/arch/arm64/kernel/kprobes-arm64.h
index 87e7891..ff8a55f 100644
--- a/arch/arm64/kernel/kprobes-arm64.h
+++ b/arch/arm64/kernel/kprobes-arm64.h
@@ -22,6 +22,8 @@ enum kprobe_insn {
 	INSN_GOOD,
 };
 
+extern kprobes_pstate_check_t * const kprobe_condition_checks[16];
+
 enum kprobe_insn __kprobes
 arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi);
 
diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
index 65e22d8..31a7894e 100644
--- a/arch/arm64/kernel/kprobes.c
+++ b/arch/arm64/kernel/kprobes.c
@@ -38,6 +38,9 @@
 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 
+static void __kprobes
+post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
+
 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 {
 	/* prepare insn slot */
@@ -54,6 +57,27 @@ static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 	p->ainsn.restore.type = RESTORE_PC;
 }
 
+static void __kprobes arch_prepare_simulate(struct kprobe *p)
+{
+	if (p->ainsn.prepare)
+		p->ainsn.prepare(p, &p->ainsn);
+
+	/* This instructions is not executed xol. No need to adjust the PC */
+	p->ainsn.restore.addr = 0;
+	p->ainsn.restore.type = NO_RESTORE;
+}
+
+static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+	if (p->ainsn.handler)
+		p->ainsn.handler((u32)p->opcode, (long)p->addr, regs);
+
+	/* single step simulated, now go for post processing */
+	post_kprobe_handler(kcb, regs);
+}
+
 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 {
 	kprobe_opcode_t insn;
@@ -72,7 +96,8 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 		return -EINVAL;
 
 	case INSN_GOOD_NO_SLOT:	/* insn need simulation */
-		return -EINVAL;
+		p->ainsn.insn = NULL;
+		break;
 
 	case INSN_GOOD:	/* instruction uses slot */
 		p->ainsn.insn = get_insn_slot();
@@ -82,7 +107,10 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 	};
 
 	/* prepare the instruction */
-	arch_prepare_ss_slot(p);
+	if (p->ainsn.insn)
+		arch_prepare_ss_slot(p);
+	else
+		arch_prepare_simulate(p);
 
 	return 0;
 }
@@ -231,7 +259,8 @@ static void __kprobes setup_singlestep(struct kprobe *p,
 		kernel_enable_single_step(regs);
 		instruction_pointer(regs) = slot;
 	} else	{
-		BUG();
+		/* insn simulation */
+		arch_simulate_insn(p, regs);
 	}
 }
 
diff --git a/arch/arm64/kernel/probes-condn-check.c b/arch/arm64/kernel/probes-condn-check.c
new file mode 100644
index 0000000..e68aa0c
--- /dev/null
+++ b/arch/arm64/kernel/probes-condn-check.c
@@ -0,0 +1,122 @@
+/*
+ * arch/arm64/kernel/probes-condn-check.c
+ *
+ * Copyright (C) 2013 Linaro Limited
+ *
+ * Copied from: arch/arm/kernel/kprobes-common.c
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * Description:
+ *
+ *  AArch64 and AArch32 shares same conditional(CNZV) flags encoding.
+ *  This file implements conditional check helpers compatible with
+ *  both AArch64 and AArch32 modes. Uprobes on v8 can handle both 32-bit
+ *  & 64-bit user-space instructions, so we abstract the common functions
+ *  in this file. While AArch64 and AArch32 specific instruction handling
+ *  are implemented in separate files, this file contains common bits.
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <asm/probes.h>
+
+static unsigned long __kprobes __check_eq(unsigned long pstate)
+{
+	return pstate & PSR_Z_BIT;
+}
+
+static unsigned long __kprobes __check_ne(unsigned long pstate)
+{
+	return (~pstate) & PSR_Z_BIT;
+}
+
+static unsigned long __kprobes __check_cs(unsigned long pstate)
+{
+	return pstate & PSR_C_BIT;
+}
+
+static unsigned long __kprobes __check_cc(unsigned long pstate)
+{
+	return (~pstate) & PSR_C_BIT;
+}
+
+static unsigned long __kprobes __check_mi(unsigned long pstate)
+{
+	return pstate & PSR_N_BIT;
+}
+
+static unsigned long __kprobes __check_pl(unsigned long pstate)
+{
+	return (~pstate) & PSR_N_BIT;
+}
+
+static unsigned long __kprobes __check_vs(unsigned long pstate)
+{
+	return pstate & PSR_V_BIT;
+}
+
+static unsigned long __kprobes __check_vc(unsigned long pstate)
+{
+	return (~pstate) & PSR_V_BIT;
+}
+
+static unsigned long __kprobes __check_hi(unsigned long pstate)
+{
+	pstate &= ~(pstate >> 1);	/* PSR_C_BIT &= ~PSR_Z_BIT */
+	return pstate & PSR_C_BIT;
+}
+
+static unsigned long __kprobes __check_ls(unsigned long pstate)
+{
+	pstate &= ~(pstate >> 1);	/* PSR_C_BIT &= ~PSR_Z_BIT */
+	return (~pstate) & PSR_C_BIT;
+}
+
+static unsigned long __kprobes __check_ge(unsigned long pstate)
+{
+	pstate ^= (pstate << 3);	/* PSR_N_BIT ^= PSR_V_BIT */
+	return (~pstate) & PSR_N_BIT;
+}
+
+static unsigned long __kprobes __check_lt(unsigned long pstate)
+{
+	pstate ^= (pstate << 3);	/* PSR_N_BIT ^= PSR_V_BIT */
+	return pstate & PSR_N_BIT;
+}
+
+static unsigned long __kprobes __check_gt(unsigned long pstate)
+{
+	/*PSR_N_BIT ^= PSR_V_BIT */
+	unsigned long temp = pstate ^ (pstate << 3);
+
+	temp |= (pstate << 1);	/*PSR_N_BIT |= PSR_Z_BIT */
+	return (~temp) & PSR_N_BIT;
+}
+
+static unsigned long __kprobes __check_le(unsigned long pstate)
+{
+	/*PSR_N_BIT ^= PSR_V_BIT */
+	unsigned long temp = pstate ^ (pstate << 3);
+
+	temp |= (pstate << 1);	/*PSR_N_BIT |= PSR_Z_BIT */
+	return temp & PSR_N_BIT;
+}
+
+static unsigned long __kprobes __check_al(unsigned long pstate)
+{
+	return true;
+}
+
+kprobes_pstate_check_t * const kprobe_condition_checks[16] = {
+	&__check_eq, &__check_ne, &__check_cs, &__check_cc,
+	&__check_mi, &__check_pl, &__check_vs, &__check_vc,
+	&__check_hi, &__check_ls, &__check_ge, &__check_lt,
+	&__check_gt, &__check_le, &__check_al, &__check_al
+};
diff --git a/arch/arm64/kernel/probes-simulate-insn.c b/arch/arm64/kernel/probes-simulate-insn.c
new file mode 100644
index 0000000..a224c91
--- /dev/null
+++ b/arch/arm64/kernel/probes-simulate-insn.c
@@ -0,0 +1,174 @@
+/*
+ * arch/arm64/kernel/probes-simulate-insn.c
+ *
+ * Copyright (C) 2013 Linaro Limited.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+#include <linux/module.h>
+
+#include "probes-simulate-insn.h"
+
+#define sign_extend(x, signbit)		\
+	((x) | (0 - ((x) & (1 << (signbit)))))
+
+#define bbl_displacement(insn)		\
+	sign_extend(((insn) & 0x3ffffff) << 2, 27)
+
+#define bcond_displacement(insn)	\
+	sign_extend(((insn >> 5) & 0x7ffff) << 2, 21)
+
+#define cbz_displacement(insn)	\
+	sign_extend(((insn >> 5) & 0x7ffff) << 2, 21)
+
+#define tbz_displacement(insn)	\
+	sign_extend(((insn >> 5) & 0x3fff) << 2, 15)
+
+#define ldr_displacement(insn)	\
+	sign_extend(((insn >> 5) & 0x7ffff) << 2, 21)
+
+
+unsigned long __kprobes check_cbz(u32 opcode, struct pt_regs *regs)
+{
+	int xn = opcode & 0x1f;
+
+	return (opcode & (1 << 31)) ?
+	    !(regs->regs[xn]) : !(regs->regs[xn] & 0xffffffff);
+}
+
+unsigned long __kprobes check_cbnz(u32 opcode, struct pt_regs *regs)
+{
+	int xn = opcode & 0x1f;
+
+	return (opcode & (1 << 31)) ?
+	    (regs->regs[xn]) : (regs->regs[xn] & 0xffffffff);
+}
+
+unsigned long __kprobes check_tbz(u32 opcode, struct pt_regs *regs)
+{
+	int xn = opcode & 0x1f;
+	int bit_pos = ((opcode & (1 << 31)) >> 26) | ((opcode >> 19) & 0x1f);
+
+	return ~((regs->regs[xn] >> bit_pos) & 0x1);
+}
+
+unsigned long __kprobes check_tbnz(u32 opcode, struct pt_regs *regs)
+{
+	int xn = opcode & 0x1f;
+	int bit_pos = ((opcode & (1 << 31)) >> 26) | ((opcode >> 19) & 0x1f);
+
+	return (regs->regs[xn] >> bit_pos) & 0x1;
+}
+
+/*
+ * instruction simulate functions
+ */
+void __kprobes simulate_none(u32 opcode, long addr, struct pt_regs *regs)
+{
+}
+
+void __kprobes
+simulate_adr_adrp(u32 opcode, long addr, struct pt_regs *regs)
+{
+	long imm, xn, val;
+
+	xn = opcode & 0x1f;
+	imm = ((opcode >> 3) & 0x1ffffc) | ((opcode >> 29) & 0x3);
+	imm = sign_extend(imm, 20);
+	if (opcode & 0x80000000)
+		val = (imm<<12) + (addr & 0xfffffffffffff000);
+	else
+		val = imm + addr;
+
+	regs->regs[xn] = val;
+
+	instruction_pointer(regs) += 4;
+}
+
+void __kprobes
+simulate_b_bl(u32 opcode, long addr, struct pt_regs *regs)
+{
+	int disp = bbl_displacement(opcode);
+
+	/* Link register is x30 */
+	if (opcode & (1 << 31))
+		regs->regs[30] = addr + 4;
+
+	instruction_pointer(regs) = addr + disp;
+}
+
+void __kprobes
+simulate_b_cond(u32 opcode, long addr, struct pt_regs *regs)
+{
+	int disp = bcond_displacement(opcode);
+
+	instruction_pointer(regs) = addr + disp;
+}
+
+void __kprobes
+simulate_br_blr_ret(u32 opcode, long addr, struct pt_regs *regs)
+{
+	int xn = (opcode >> 5) & 0x1f;
+
+	/* Link register is x30 */
+	if (((opcode >> 21) & 0x3) == 1)
+		regs->regs[30] = addr + 4;
+
+	instruction_pointer(regs) = regs->regs[xn];
+}
+
+void __kprobes
+simulate_cbz_cbnz(u32 opcode, long addr, struct pt_regs *regs)
+{
+	int disp = cbz_displacement(opcode);
+
+	instruction_pointer(regs) = addr + disp;
+}
+
+void __kprobes
+simulate_tbz_tbnz(u32 opcode, long addr, struct pt_regs *regs)
+{
+	int disp = tbz_displacement(opcode);
+
+	instruction_pointer(regs) = addr + disp;
+}
+
+void __kprobes
+simulate_ldr_literal(u32 opcode, long addr, struct pt_regs *regs)
+{
+	u64 *load_addr;
+	int xn = opcode & 0x1f;
+	int disp = ldr_displacement(opcode);
+
+	load_addr = (u64 *) (addr + disp);
+
+	if (opcode & (1 << 30))	/* x0-x31 */
+		regs->regs[xn] = *load_addr;
+	else			/* w0-w31 */
+		*(u32 *) (&regs->regs[xn]) = (*(u32 *) (load_addr));
+
+	instruction_pointer(regs) += 4;
+}
+
+void __kprobes
+simulate_ldrsw_literal(u32 opcode, long addr, struct pt_regs *regs)
+{
+	s32 *load_addr;
+	int xn = opcode & 0x1f;
+	int disp = ldr_displacement(opcode);
+
+	load_addr = (s32 *) (addr + disp);
+	regs->regs[xn] = *load_addr;
+
+	instruction_pointer(regs) += 4;
+}
diff --git a/arch/arm64/kernel/probes-simulate-insn.h b/arch/arm64/kernel/probes-simulate-insn.h
new file mode 100644
index 0000000..406f5c2
--- /dev/null
+++ b/arch/arm64/kernel/probes-simulate-insn.h
@@ -0,0 +1,33 @@
+/*
+ * arch/arm64/kernel/probes-simulate-insn.h
+ *
+ * Copyright (C) 2013 Linaro Limited
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#ifndef _ARM_KERNEL_PROBES_SIMULATE_INSN_H
+#define _ARM_KERNEL_PROBES_SIMULATE_INSN_H
+
+unsigned long check_cbz(u32 opcode, struct pt_regs *regs);
+unsigned long check_cbnz(u32 opcode, struct pt_regs *regs);
+unsigned long check_tbz(u32 opcode, struct pt_regs *regs);
+unsigned long check_tbnz(u32 opcode, struct pt_regs *regs);
+void simulate_none(u32 opcode, long addr, struct pt_regs *regs);
+void simulate_adr_adrp(u32 opcode, long addr, struct pt_regs *regs);
+void simulate_b_bl(u32 opcode, long addr, struct pt_regs *regs);
+void simulate_b_cond(u32 opcode, long addr, struct pt_regs *regs);
+void simulate_br_blr_ret(u32 opcode, long addr, struct pt_regs *regs);
+void simulate_cbz_cbnz(u32 opcode, long addr, struct pt_regs *regs);
+void simulate_tbz_tbnz(u32 opcode, long addr, struct pt_regs *regs);
+void simulate_ldr_literal(u32 opcode, long addr, struct pt_regs *regs);
+void simulate_ldrsw_literal(u32 opcode, long addr, struct pt_regs *regs);
+
+#endif /* _ARM_KERNEL_PROBES_SIMULATE_INSN_H */
-- 
1.8.1.2


^ permalink raw reply	[flat|nested] 21+ messages in thread

* [PATCH v4 5/6] arm64: Add kernel return probes support(kretprobes)
  2015-01-11  4:03 [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support David Long
                   ` (3 preceding siblings ...)
  2015-01-11  4:03 ` [PATCH v4 4/6] arm64: Kprobes instruction simulation support David Long
@ 2015-01-11  4:03 ` David Long
  2015-01-12 14:01   ` Steve Capper
  2015-01-11  4:03 ` [PATCH v4 6/6] kprobes: Add arm64 case in kprobe example module David Long
  2015-01-12 14:09 ` [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support Steve Capper
  6 siblings, 1 reply; 21+ messages in thread
From: David Long @ 2015-01-11  4:03 UTC (permalink / raw)
  To: linux-arm-kernel, Russell King
  Cc: Sandeepa Prabhu, William Cohen, Steve Capper, Catalin Marinas,
	Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>

AArch64 ISA does not have instructions to pop the PC register
value from the stack(like ARM v7 has ldmia {...,pc}) without using
one of the general purpose registers. This means return probes
cannot return to the actual return address directly without
modifying register context, and without trapping into debug exception.

So, like many other architectures, we prepare a global routine
with NOPs which serve as a trampoline to hack away the
function return address by placing an extra kprobe on the
trampoline entry.

The pre-handler of this special 'trampoline' kprobe executes the return
probe handler functions and restores original return address in ELR_EL1.
This way the saved pt_regs still hold the original register context to be
carried back to the probed kernel function.

Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
Signed-off-by: David A. Long <dave.long@linaro.org>
---
 arch/arm64/Kconfig               |   1 +
 arch/arm64/include/asm/kprobes.h |   1 +
 arch/arm64/kernel/kprobes.c      | 114 ++++++++++++++++++++++++++++++++++++++-
 3 files changed, 115 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b3f61ba..de4f056 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -68,6 +68,7 @@ config ARM64
 	select HAVE_RCU_TABLE_FREE
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_KPROBES if !XIP_KERNEL
+	select HAVE_KRETPROBES if HAVE_KPROBES
 	select IRQ_DOMAIN
 	select MODULES_USE_ELF_RELA
 	select NO_BOOTMEM
diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index b35d3b9..a2de3b8 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -56,5 +56,6 @@ void arch_remove_kprobe(struct kprobe *);
 int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
 int kprobe_exceptions_notify(struct notifier_block *self,
 			     unsigned long val, void *data);
+void kretprobe_trampoline(void);
 
 #endif /* _ARM_KPROBES_H */
diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
index 31a7894e..cd1069c 100644
--- a/arch/arm64/kernel/kprobes.c
+++ b/arch/arm64/kernel/kprobes.c
@@ -559,6 +559,117 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 	return 0;
 }
 
+/*
+ * Kretprobes: kernel return probes handling
+ *
+ * AArch64 mode does not support popping the PC value from the
+ * stack like on ARM 32-bit (ldmia {..,pc}), so atleast one
+ * register need to be used to achieve branching/return.
+ * It means return probes cannot return back to the original
+ * return address directly without modifying the register context.
+ *
+ * So like other architectures, we prepare a global routine
+ * with NOPs, which serve as trampoline address that hack away the
+ * function return, with the exact register context.
+ * Placing a kprobe on trampoline routine entry will trap again to
+ * execute return probe handlers and restore original return address
+ * in ELR_EL1, this way saved pt_regs still hold the original
+ * register values to be carried back to the caller.
+ */
+static void __used kretprobe_trampoline_holder(void)
+{
+	asm volatile (".global kretprobe_trampoline\n"
+			"kretprobe_trampoline:\n"
+			"NOP\n\t"
+			"NOP\n\t");
+}
+
+static int __kprobes
+trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
+{
+	struct kretprobe_instance *ri = NULL;
+	struct hlist_head *head, empty_rp;
+	struct hlist_node *tmp;
+	unsigned long flags, orig_ret_addr = 0;
+	unsigned long trampoline_address =
+		(unsigned long)&kretprobe_trampoline;
+
+	INIT_HLIST_HEAD(&empty_rp);
+	kretprobe_hash_lock(current, &head, &flags);
+
+	/*
+	 * It is possible to have multiple instances associated with a given
+	 * task either because multiple functions in the call path have
+	 * a return probe installed on them, and/or more than one return
+	 * probe was registered for a target function.
+	 *
+	 * We can handle this because:
+	 *     - instances are always inserted at the head of the list
+	 *     - when multiple return probes are registered for the same
+	 *       function, the first instance's ret_addr will point to the
+	 *       real return address, and all the rest will point to
+	 *       kretprobe_trampoline
+	 */
+	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
+		if (ri->task != current)
+			/* another task is sharing our hash bucket */
+			continue;
+
+		if (ri->rp && ri->rp->handler) {
+			__this_cpu_write(current_kprobe, &ri->rp->kp);
+			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+			ri->rp->handler(ri, regs);
+			__this_cpu_write(current_kprobe, NULL);
+		}
+
+		orig_ret_addr = (unsigned long)ri->ret_addr;
+		recycle_rp_inst(ri, &empty_rp);
+
+		if (orig_ret_addr != trampoline_address)
+			/*
+			 * This is the real return address. Any other
+			 * instances associated with this task are for
+			 * other calls deeper on the call stack
+			 */
+			break;
+	}
+
+	kretprobe_assert(ri, orig_ret_addr, trampoline_address);
+	/* restore the original return address */
+	instruction_pointer(regs) = orig_ret_addr;
+	reset_current_kprobe();
+	kretprobe_hash_unlock(current, &flags);
+
+	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
+		hlist_del(&ri->hlist);
+		kfree(ri);
+	}
+
+	kprobes_restore_local_irqflag(regs);
+
+	/* return 1 so that post handlers not called */
+	return 1;
+}
+
+void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
+				      struct pt_regs *regs)
+{
+	ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
+
+	/* replace return addr (x30) with trampoline */
+	regs->regs[30] = (long)&kretprobe_trampoline;
+}
+
+static struct kprobe trampoline = {
+	.addr = (kprobe_opcode_t *) &kretprobe_trampoline,
+	.pre_handler = trampoline_probe_handler
+};
+
+int __kprobes arch_trampoline_kprobe(struct kprobe *p)
+{
+	return p->addr == (kprobe_opcode_t *) &kretprobe_trampoline;
+}
+
 /* Break Handler hook */
 static struct break_hook kprobes_break_hook = {
 	.esr_mask = BRK64_ESR_MASK,
@@ -576,5 +687,6 @@ int __init arch_init_kprobes(void)
 	register_break_hook(&kprobes_break_hook);
 	register_step_hook(&kprobes_step_hook);
 
-	return 0;
+	/* register trampoline for kret probe */
+	return register_kprobe(&trampoline);
 }
-- 
1.8.1.2


^ permalink raw reply	[flat|nested] 21+ messages in thread

* [PATCH v4 6/6] kprobes: Add arm64 case in kprobe example module
  2015-01-11  4:03 [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support David Long
                   ` (4 preceding siblings ...)
  2015-01-11  4:03 ` [PATCH v4 5/6] arm64: Add kernel return probes support(kretprobes) David Long
@ 2015-01-11  4:03 ` David Long
  2015-01-12 14:09 ` [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support Steve Capper
  6 siblings, 0 replies; 21+ messages in thread
From: David Long @ 2015-01-11  4:03 UTC (permalink / raw)
  To: linux-arm-kernel, Russell King
  Cc: Sandeepa Prabhu, William Cohen, Steve Capper, Catalin Marinas,
	Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>

Add info prints in sample kprobe handlers for ARM64

Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
---
 samples/kprobes/kprobe_example.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/samples/kprobes/kprobe_example.c b/samples/kprobes/kprobe_example.c
index 366db1a..51d459c 100644
--- a/samples/kprobes/kprobe_example.c
+++ b/samples/kprobes/kprobe_example.c
@@ -42,6 +42,10 @@ static int handler_pre(struct kprobe *p, struct pt_regs *regs)
 			" ex1 = 0x%lx\n",
 		p->addr, regs->pc, regs->ex1);
 #endif
+#ifdef CONFIG_ARM64
+	pr_info("pre_handler: p->addr = 0x%p, pc = 0x%lx\n",
+		p->addr, (long)regs->pc);
+#endif
 
 	/* A dump_stack() here will give a stack backtrace */
 	return 0;
@@ -67,6 +71,10 @@ static void handler_post(struct kprobe *p, struct pt_regs *regs,
 	printk(KERN_INFO "post_handler: p->addr = 0x%p, ex1 = 0x%lx\n",
 		p->addr, regs->ex1);
 #endif
+#ifdef CONFIG_ARM64
+	pr_info("post_handler: p->addr = 0x%p, pc = 0x%lx\n",
+		p->addr, (long)regs->pc);
+#endif
 }
 
 /*
-- 
1.8.1.2


^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 1/6] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature
  2015-01-11  4:03 ` [PATCH v4 1/6] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature David Long
@ 2015-01-12 12:51   ` Steve Capper
  2015-01-15  7:07     ` Masami Hiramatsu
  0 siblings, 1 reply; 21+ messages in thread
From: Steve Capper @ 2015-01-12 12:51 UTC (permalink / raw)
  To: David Long
  Cc: linux-arm-kernel, Russell King, Sandeepa Prabhu, William Cohen,
	Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

On Sat, Jan 10, 2015 at 11:03:16PM -0500, David Long wrote:
> From: "David A. Long" <dave.long@linaro.org>
> 
> Add HAVE_REGS_AND_STACK_ACCESS_API feature for arm64.
> 
> Signed-off-by: David A. Long <dave.long@linaro.org>
> ---
>  arch/arm64/Kconfig                   |   1 +
>  arch/arm64/include/asm/ptrace.h      |  29 +++++++++
>  arch/arm64/include/uapi/asm/ptrace.h |  36 +++++++++++
>  arch/arm64/kernel/ptrace.c           | 119 +++++++++++++++++++++++++++++++++++
>  4 files changed, 185 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index b1f9a20..12b3fd6 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -64,6 +64,7 @@ config ARM64
>  	select HAVE_PERF_EVENTS
>  	select HAVE_PERF_REGS
>  	select HAVE_PERF_USER_STACK_DUMP
> +	select HAVE_REGS_AND_STACK_ACCESS_API
>  	select HAVE_RCU_TABLE_FREE
>  	select HAVE_SYSCALL_TRACEPOINTS
>  	select IRQ_DOMAIN
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index 41ed9e1..3613e49 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -111,6 +111,8 @@ struct pt_regs {
>  	u64 syscallno;
>  };
>  
> +#define MAX_REG_OFFSET (sizeof(struct user_pt_regs) - sizeof(u64))
> +
>  #define arch_has_single_step()	(1)
>  
>  #ifdef CONFIG_COMPAT
> @@ -139,11 +141,38 @@ struct pt_regs {
>  #define user_stack_pointer(regs) \
>  	(!compat_user_mode(regs) ? (regs)->sp : (regs)->compat_sp)
>  
> +/**
> + * regs_get_register() - get register value from its offset
> + * @regs:	   pt_regs from which register value is gotten
> + * @offset:    offset number of the register.
> + *
> + * regs_get_register returns the value of a register whose offset from @regs.
> + * The @offset is the offset of the register in struct pt_regs.
> + * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
> + */
> +static inline u64 regs_get_register(struct pt_regs *regs,
> +					      unsigned int offset)
> +{
> +	if (unlikely(offset > MAX_REG_OFFSET))
> +		return 0;
> +	return *(u64 *)((u64)regs + offset);
> +}
> +
> +/* Valid only for Kernel mode traps. */
> +static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
> +{
> +	return regs->ARM_sp;
> +}
> +
>  static inline unsigned long regs_return_value(struct pt_regs *regs)
>  {
>  	return regs->regs[0];
>  }
>  
> +extern int regs_query_register_offset(const char *name);
> +extern unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
> +					       unsigned int n);
> +
>  /*
>   * Are the current registers suitable for user mode? (used to maintain
>   * security in signal handlers)
> diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
> index 6913643..700d28b 100644
> --- a/arch/arm64/include/uapi/asm/ptrace.h
> +++ b/arch/arm64/include/uapi/asm/ptrace.h
> @@ -61,6 +61,42 @@
>  
>  #ifndef __ASSEMBLY__
>  
> +#define ARM_cpsr	pstate
> +#define ARM_pc		pc
> +#define ARM_sp		sp
> +#define ARM_lr		regs[30]
> +#define ARM_fp		regs[29]
> +#define ARM_x28		regs[28]
> +#define ARM_x27		regs[27]
> +#define ARM_x26		regs[26]
> +#define ARM_x25		regs[25]
> +#define ARM_x24		regs[24]
> +#define ARM_x23		regs[23]
> +#define ARM_x22		regs[22]
> +#define ARM_x21		regs[21]
> +#define ARM_x20		regs[20]
> +#define ARM_x19		regs[19]
> +#define ARM_x18		regs[18]
> +#define ARM_ip1		regs[17]
> +#define ARM_ip0		regs[16]
> +#define ARM_x15		regs[15]
> +#define ARM_x14		regs[14]
> +#define ARM_x13		regs[13]
> +#define ARM_x12		regs[12]
> +#define ARM_x11		regs[11]
> +#define ARM_x10		regs[10]
> +#define ARM_x9		regs[9]
> +#define ARM_x8		regs[8]
> +#define ARM_x7		regs[7]
> +#define ARM_x6		regs[6]
> +#define ARM_x5		regs[5]
> +#define ARM_x4		regs[4]
> +#define ARM_x3		regs[3]
> +#define ARM_x2		regs[2]
> +#define ARM_x1		regs[1]
> +#define ARM_x0		regs[0]
> +#define ARM_ORIG_x0	orig_x0
> +
>  /*
>   * User structures for general purpose, floating point and debug registers.
>   */
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index d882b83..9115b25 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -48,6 +48,125 @@
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/syscalls.h>
>  
> +struct pt_regs_offset {
> +	const char *name;
> +	int offset;
> +};
> +
> +#define REG_OFFSET_NAME(r) \
> +	{.name = #r, .offset = offsetof(struct pt_regs, ARM_##r)}
> +#define REG_OFFSET_END {.name = NULL, .offset = 0}
> +
> +static const struct pt_regs_offset regoffset_table[] = {
> +	REG_OFFSET_NAME(x0),
> +	REG_OFFSET_NAME(x1),
> +	REG_OFFSET_NAME(x2),
> +	REG_OFFSET_NAME(x3),
> +	REG_OFFSET_NAME(x4),
> +	REG_OFFSET_NAME(x5),
> +	REG_OFFSET_NAME(x6),
> +	REG_OFFSET_NAME(x7),
> +	REG_OFFSET_NAME(x8),
> +	REG_OFFSET_NAME(x9),
> +	REG_OFFSET_NAME(x10),
> +	REG_OFFSET_NAME(x11),
> +	REG_OFFSET_NAME(x12),
> +	REG_OFFSET_NAME(x13),
> +	REG_OFFSET_NAME(x14),
> +	REG_OFFSET_NAME(x15),
> +	REG_OFFSET_NAME(ip0),
> +	REG_OFFSET_NAME(ip1),
> +	REG_OFFSET_NAME(x18),
> +	REG_OFFSET_NAME(x19),
> +	REG_OFFSET_NAME(x20),
> +	REG_OFFSET_NAME(x21),
> +	REG_OFFSET_NAME(x22),
> +	REG_OFFSET_NAME(x23),
> +	REG_OFFSET_NAME(x24),
> +	REG_OFFSET_NAME(x25),
> +	REG_OFFSET_NAME(x26),
> +	REG_OFFSET_NAME(x27),
> +	REG_OFFSET_NAME(x28),
> +	REG_OFFSET_NAME(fp),
> +	REG_OFFSET_NAME(lr),
> +/*
> +	REG_OFFSET_NAME(ip),
> +*/

Should this comment block be removed?

> +	REG_OFFSET_NAME(sp),
> +	REG_OFFSET_NAME(pc),
> +	REG_OFFSET_NAME(cpsr),
> +	REG_OFFSET_NAME(ORIG_x0),
> +	REG_OFFSET_END,
> +};
> +
> +/**
> + * regs_query_register_offset() - query register offset from its name
> + * @name:	the name of a register
> + *
> + * regs_query_register_offset() returns the offset of a register in struct
> + * pt_regs from its name. If the name is invalid, this returns -EINVAL;
> + */
> +int regs_query_register_offset(const char *name)
> +{
> +	const struct pt_regs_offset *roff;
> +
> +	for (roff = regoffset_table; roff->name != NULL; roff++)
> +		if (!strcmp(roff->name, name))
> +			return roff->offset;
> +	return -EINVAL;
> +}
> +
> +/**
> + * regs_query_register_name() - query register name from its offset
> + * @offset:	the offset of a register in struct pt_regs.
> + *
> + * regs_query_register_name() returns the name of a register from its
> + * offset in struct pt_regs. If the @offset is invalid, this returns NULL;
> + */
> +const char *regs_query_register_name(unsigned int offset)
> +{
> +	const struct pt_regs_offset *roff;
> +
> +	for (roff = regoffset_table; roff->name != NULL; roff++)
> +		if (roff->offset == offset)
> +			return roff->name;
> +	return NULL;
> +}
> +
> +/**
> + * regs_within_kernel_stack() - check the address in the stack
> + * @regs:      pt_regs which contains kernel stack pointer.
> + * @addr:      address which is checked.
> + *
> + * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
> + * If @addr is within the kernel stack, it returns true. If not, returns false.
> + */
> +bool regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
> +{
> +	return ((addr & ~(THREAD_SIZE - 1))  ==
> +		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1)));
> +}
> +
> +/**
> + * regs_get_kernel_stack_nth() - get Nth entry of the stack
> + * @regs:	pt_regs which contains kernel stack pointer.
> + * @n:		stack entry number.
> + *
> + * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
> + * is specified by @regs. If the @n th entry is NOT in the kernel stack,
> + * this returns 0.
> + */
> +unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
> +{
> +	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
> +
> +	addr += n;
> +	if (regs_within_kernel_stack(regs, (unsigned long)addr))
> +		return *addr;
> +	else
> +		return 0;
> +}
> +
>  /*
>   * TODO: does not yet catch signals sent when the child dies.
>   * in exit.c or in signal.c.
> -- 
> 1.8.1.2
> 

^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 3/6] arm64: Kprobes with single stepping support
  2015-01-11  4:03 ` [PATCH v4 3/6] arm64: Kprobes with single stepping support David Long
@ 2015-01-12 13:31   ` Steve Capper
  2015-01-14  9:30   ` Pratyush Anand
  1 sibling, 0 replies; 21+ messages in thread
From: Steve Capper @ 2015-01-12 13:31 UTC (permalink / raw)
  To: David Long
  Cc: linux-arm-kernel, Russell King, Sandeepa Prabhu, William Cohen,
	Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

On Sat, Jan 10, 2015 at 11:03:18PM -0500, David Long wrote:
> From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
> 
> Add support for basic kernel probes(kprobes) and jump probes
> (jprobes) for ARM64.
> 
> Kprobes will utilize software breakpoint and single step debug
> exceptions supported on ARM v8.
> 
> Software breakpoint is placed at the probe address to trap the
> kernel execution into kprobe handler.
> 
> ARM v8 supports single stepping to be enabled while exception return
> (ERET) with next PC in exception return address (ELR_EL1). The
> kprobe handler prepares an executable memory slot for out-of-line
> execution with a copy of the original instruction being probed, and
> enables single stepping from the instruction slot. With this scheme,
> the instruction is executed with the exact same register context
> 'except PC' that points to instruction slot.
> 
> Debug mask(PSTATE.D) is enabled only when single stepping a recursive
> kprobe, e.g.: during kprobes reenter so that probed instruction can be
> single stepped within the kprobe handler -exception- context.
> The recursion depth of kprobe is always 2, i.e. upon probe re-entry,
> any further re-entry is prevented by not calling handlers and the case
> counted as a missed kprobe).
> 
> Single stepping from slot has a drawback on PC-relative accesses
> like branching and symbolic literals access as offset from new PC
> (slot address) may not be ensured to fit in immediate value of
> opcode. Such instructions needs simulation, so reject
> probing such instructions.
> 
> Instructions generating exceptions or cpu mode change are rejected,
> and not allowed to insert probe for these instructions.
> 
> Instructions using Exclusive Monitor are rejected too.
> 
> System instructions are mostly enabled for stepping, except MSR
> immediate that updates "daif" flags in PSTATE, which are not safe
> for probing.
> 
> Changes since v3:
> from David Long:
> 1) Removed unnecessary addtion of NOP after out-of-line instruction.
> 2) Replaced table-driven instruction parsing with calls to external
>    test functions.
> from Steve Capper:
> 3) Disable local irq while executing out of line instruction.
> 
> Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
> Signed-off-by: Steve Capper <steve.capper@linaro.org>
> Signed-off-by: David A. Long <dave.long@linaro.org>
> ---
>  arch/arm64/Kconfig                |   1 +
>  arch/arm64/include/asm/kprobes.h  |  60 +++++
>  arch/arm64/include/asm/probes.h   |  50 ++++
>  arch/arm64/include/asm/ptrace.h   |   3 +-
>  arch/arm64/kernel/Makefile        |   1 +
>  arch/arm64/kernel/kprobes-arm64.c |  65 +++++
>  arch/arm64/kernel/kprobes-arm64.h |  28 ++
>  arch/arm64/kernel/kprobes.c       | 551 ++++++++++++++++++++++++++++++++++++++
>  arch/arm64/kernel/kprobes.h       |  30 +++
>  arch/arm64/kernel/vmlinux.lds.S   |   1 +
>  10 files changed, 789 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/kprobes.h
>  create mode 100644 arch/arm64/include/asm/probes.h
>  create mode 100644 arch/arm64/kernel/kprobes-arm64.c
>  create mode 100644 arch/arm64/kernel/kprobes-arm64.h
>  create mode 100644 arch/arm64/kernel/kprobes.c
>  create mode 100644 arch/arm64/kernel/kprobes.h
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 12b3fd6..b3f61ba 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -67,6 +67,7 @@ config ARM64
>  	select HAVE_REGS_AND_STACK_ACCESS_API
>  	select HAVE_RCU_TABLE_FREE
>  	select HAVE_SYSCALL_TRACEPOINTS
> +	select HAVE_KPROBES if !XIP_KERNEL

I don't think we need "if !XIP_KERNEL" for arm64?

>  	select IRQ_DOMAIN
>  	select MODULES_USE_ELF_RELA
>  	select NO_BOOTMEM
> diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
> new file mode 100644
> index 0000000..b35d3b9
> --- /dev/null
> +++ b/arch/arm64/include/asm/kprobes.h
> @@ -0,0 +1,60 @@
> +/*
> + * arch/arm64/include/asm/kprobes.h
> + *
> + * Copyright (C) 2013 Linaro Limited
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +
> +#ifndef _ARM_KPROBES_H
> +#define _ARM_KPROBES_H
> +
> +#include <linux/types.h>
> +#include <linux/ptrace.h>
> +#include <linux/percpu.h>
> +
> +#define __ARCH_WANT_KPROBES_INSN_SLOT
> +#define MAX_INSN_SIZE			1
> +#define MAX_STACK_SIZE			128
> +
> +#define flush_insn_slot(p)		do { } while (0)
> +#define kretprobe_blacklist_size	0
> +
> +#include <asm/probes.h>
> +
> +struct prev_kprobe {
> +	struct kprobe *kp;
> +	unsigned int status;
> +};
> +
> +/* Single step context for kprobe */
> +struct kprobe_step_ctx {
> +#define KPROBES_STEP_NONE	0x0
> +#define KPROBES_STEP_PENDING	0x1
> +	unsigned long ss_status;
> +	unsigned long match_addr;
> +};
> +
> +/* per-cpu kprobe control block */
> +struct kprobe_ctlblk {
> +	unsigned int kprobe_status;
> +	unsigned long saved_irqflag;
> +	struct prev_kprobe prev_kprobe;
> +	struct kprobe_step_ctx ss_ctx;
> +	struct pt_regs jprobe_saved_regs;
> +	char jprobes_stack[MAX_STACK_SIZE];
> +};
> +
> +void arch_remove_kprobe(struct kprobe *);
> +int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
> +int kprobe_exceptions_notify(struct notifier_block *self,
> +			     unsigned long val, void *data);
> +
> +#endif /* _ARM_KPROBES_H */
> diff --git a/arch/arm64/include/asm/probes.h b/arch/arm64/include/asm/probes.h
> new file mode 100644
> index 0000000..9dba74d
> --- /dev/null
> +++ b/arch/arm64/include/asm/probes.h
> @@ -0,0 +1,50 @@
> +/*
> + * arch/arm64/include/asm/probes.h
> + *
> + * Copyright (C) 2013 Linaro Limited
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +#ifndef _ARM_PROBES_H
> +#define _ARM_PROBES_H
> +
> +struct kprobe;
> +struct arch_specific_insn;
> +
> +typedef u32 kprobe_opcode_t;
> +typedef unsigned long (kprobes_pstate_check_t)(unsigned long);
> +typedef unsigned long
> +(kprobes_condition_check_t)(struct kprobe *p, struct pt_regs *);
> +typedef void
> +(kprobes_prepare_t)(struct kprobe *, struct arch_specific_insn *);
> +typedef void (kprobes_handler_t) (u32 opcode, long addr, struct pt_regs *);
> +
> +enum pc_restore_type {
> +	NO_RESTORE,
> +	RESTORE_PC,
> +};
> +
> +struct kprobe_pc_restore {
> +	enum pc_restore_type type;
> +	unsigned long addr;
> +};
> +
> +/* architecture specific copy of original instruction */
> +struct arch_specific_insn {
> +	kprobe_opcode_t *insn;
> +	kprobes_pstate_check_t *pstate_cc;
> +	kprobes_condition_check_t *check_condn;
> +	kprobes_prepare_t *prepare;
> +	kprobes_handler_t *handler;
> +	/* restore address after step xol */
> +	struct kprobe_pc_restore restore;
> +};
> +
> +#endif
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index 3613e49..e436b49 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -203,7 +203,8 @@ static inline int valid_user_regs(struct user_pt_regs *regs)
>  	return 0;
>  }
>  
> -#define instruction_pointer(regs)	((unsigned long)(regs)->pc)
> +#define instruction_pointer(regs)	((regs)->pc)
> +#define stack_pointer(regs)		((regs)->sp)
>  
>  #ifdef CONFIG_SMP
>  extern unsigned long profile_pc(struct pt_regs *regs);
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index eaa77ed..6ca9fc0 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -31,6 +31,7 @@ arm64-obj-$(CONFIG_ARM64_CPU_SUSPEND)	+= sleep.o suspend.o
>  arm64-obj-$(CONFIG_CPU_IDLE)		+= cpuidle.o
>  arm64-obj-$(CONFIG_JUMP_LABEL)		+= jump_label.o
>  arm64-obj-$(CONFIG_KGDB)		+= kgdb.o
> +arm64-obj-$(CONFIG_KPROBES)		+= kprobes.o kprobes-arm64.o
>  arm64-obj-$(CONFIG_EFI)			+= efi.o efi-stub.o efi-entry.o
>  arm64-obj-$(CONFIG_PCI)			+= pci.o
>  arm64-obj-$(CONFIG_ARMV8_DEPRECATED)	+= armv8_deprecated.o
> diff --git a/arch/arm64/kernel/kprobes-arm64.c b/arch/arm64/kernel/kprobes-arm64.c
> new file mode 100644
> index 0000000..a698bd3
> --- /dev/null
> +++ b/arch/arm64/kernel/kprobes-arm64.c
> @@ -0,0 +1,65 @@
> +/*
> + * arch/arm64/kernel/kprobes-arm64.c
> + *
> + * Copyright (C) 2013 Linaro Limited.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/kprobes.h>
> +#include <linux/module.h>
> +#include <asm/kprobes.h>
> +#include <asm/insn.h>
> +
> +#include "kprobes-arm64.h"
> +
> +static bool aarch64_insn_is_steppable(u32 insn)
> +{
> +	if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
> +		if (aarch64_insn_is_branch(insn))
> +			return false;
> +
> +		/* modification of daif creates issues */
> +		if (aarch64_insn_is_msr_daif(insn))
> +			return false;
> +
> +		if (aarch64_insn_is_hint(insn))
> +			return aarch64_insn_is_nop(insn);
> +
> +		return true;
> +	}
> +
> +	if (aarch64_insn_uses_literal(insn))
> +		return false;
> +
> +	if (aarch64_insn_is_exclusive(insn))
> +		return false;
> +
> +	return true;
> +}
> +
> +/* Return:
> + *   INSN_REJECTED     If instruction is one not allowed to kprobe,
> + *   INSN_GOOD         If instruction is supported and uses instruction slot,
> + *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
> + */
> +enum kprobe_insn __kprobes
> +arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
> +{
> +	/*
> +	 * Instructions reading or modifying the PC won't work from the XOL
> +	 * slot.
> +	 */
> +	if (aarch64_insn_is_steppable(insn))
> +		return INSN_GOOD;
> +	else
> +		return INSN_REJECTED;
> +}
> diff --git a/arch/arm64/kernel/kprobes-arm64.h b/arch/arm64/kernel/kprobes-arm64.h
> new file mode 100644
> index 0000000..87e7891
> --- /dev/null
> +++ b/arch/arm64/kernel/kprobes-arm64.h
> @@ -0,0 +1,28 @@
> +/*
> + * arch/arm64/kernel/kprobes-arm64.h
> + *
> + * Copyright (C) 2013 Linaro Limited.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +
> +#ifndef _ARM_KERNEL_KPROBES_ARM64_H
> +#define _ARM_KERNEL_KPROBES_ARM64_H
> +
> +enum kprobe_insn {
> +	INSN_REJECTED,
> +	INSN_GOOD_NO_SLOT,
> +	INSN_GOOD,
> +};
> +
> +enum kprobe_insn __kprobes
> +arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi);
> +
> +#endif /* _ARM_KERNEL_KPROBES_ARM64_H */
> diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
> new file mode 100644
> index 0000000..65e22d8
> --- /dev/null
> +++ b/arch/arm64/kernel/kprobes.c
> @@ -0,0 +1,551 @@
> +/*
> + * arch/arm64/kernel/kprobes.c
> + *
> + * Kprobes support for ARM64
> + *
> + * Copyright (C) 2013 Linaro Limited.
> + * Author: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + *
> + */
> +#include <linux/kernel.h>
> +#include <linux/kprobes.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/stop_machine.h>
> +#include <linux/stringify.h>
> +#include <asm/traps.h>
> +#include <asm/ptrace.h>
> +#include <asm/cacheflush.h>
> +#include <asm/debug-monitors.h>
> +#include <asm/system_misc.h>
> +#include <asm/insn.h>
> +
> +#include "kprobes.h"
> +#include "kprobes-arm64.h"
> +
> +#define MIN_STACK_SIZE(addr)	min((unsigned long)MAX_STACK_SIZE,	\
> +	(unsigned long)current_thread_info() + THREAD_START_SP - (addr))
> +
> +DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
> +DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> +
> +static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
> +{
> +	/* prepare insn slot */
> +	p->ainsn.insn[0] = p->opcode;
> +
> +	flush_icache_range((uintptr_t) (p->ainsn.insn),
> +			   (uintptr_t) (p->ainsn.insn) + MAX_INSN_SIZE);
> +
> +	/*
> +	 * Needs restoring of return address after stepping xol.
> +	 */
> +	p->ainsn.restore.addr = (unsigned long) p->addr +
> +	  sizeof(kprobe_opcode_t);
> +	p->ainsn.restore.type = RESTORE_PC;
> +}
> +
> +int __kprobes arch_prepare_kprobe(struct kprobe *p)
> +{
> +	kprobe_opcode_t insn;
> +	unsigned long probe_addr = (unsigned long)p->addr;
> +
> +	/* copy instruction */
> +	insn = *p->addr;
> +	p->opcode = insn;
> +
> +	if (in_exception_text(probe_addr))
> +		return -EINVAL;
> +
> +	/* decode instruction */
> +	switch (arm_kprobe_decode_insn(insn, &p->ainsn)) {
> +	case INSN_REJECTED:	/* insn not supported */
> +		return -EINVAL;
> +
> +	case INSN_GOOD_NO_SLOT:	/* insn need simulation */
> +		return -EINVAL;
> +
> +	case INSN_GOOD:	/* instruction uses slot */
> +		p->ainsn.insn = get_insn_slot();
> +		if (!p->ainsn.insn)
> +			return -ENOMEM;
> +		break;
> +	};
> +
> +	/* prepare the instruction */
> +	arch_prepare_ss_slot(p);
> +
> +	return 0;
> +}
> +
> +static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
> +{
> +	void *addrs[1];
> +	u32 insns[1];
> +
> +	addrs[0] = (void *)addr;
> +	insns[0] = (u32)opcode;
> +
> +	return aarch64_insn_patch_text_sync(addrs, insns, 1);
> +}
> +
> +/* arm kprobe: install breakpoint in text */
> +void __kprobes arch_arm_kprobe(struct kprobe *p)
> +{
> +	patch_text(p->addr, BRK64_OPCODE_KPROBES);
> +}
> +
> +/* disarm kprobe: remove breakpoint from text */
> +void __kprobes arch_disarm_kprobe(struct kprobe *p)
> +{
> +	patch_text(p->addr, p->opcode);
> +}
> +
> +void __kprobes arch_remove_kprobe(struct kprobe *p)
> +{
> +	if (p->ainsn.insn) {
> +		free_insn_slot(p->ainsn.insn, 0);
> +		p->ainsn.insn = NULL;
> +	}
> +}
> +
> +static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> +	kcb->prev_kprobe.kp = kprobe_running();
> +	kcb->prev_kprobe.status = kcb->kprobe_status;
> +}
> +
> +static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> +	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
> +	kcb->kprobe_status = kcb->prev_kprobe.status;
> +}
> +
> +static void __kprobes set_current_kprobe(struct kprobe *p)
> +{
> +	__this_cpu_write(current_kprobe, p);
> +}
> +
> +/*
> + * Debug flag (D-flag) is disabled upon exception entry.
> + * Kprobes need to unmask D-flag -ONLY- in case of recursive
> + * probe i.e. when probe hit from kprobe handler context upon
> + * executing the pre/post handlers. In this case we return with
> + * D-flag unmasked so that single-stepping can be carried-out.
> + *
> + * Keep D-flag masked in all other cases.
> + */
> +static void __kprobes
> +spsr_set_debug_flag(struct pt_regs *regs, int mask)
> +{
> +	unsigned long spsr = regs->pstate;
> +
> +	if (mask)
> +		spsr |= PSR_D_BIT;
> +	else
> +		spsr &= ~PSR_D_BIT;
> +
> +	regs->pstate = spsr;
> +}
> +
> +/*
> + * Interrupt needs to be disabled for the duration from probe hitting
> + * breakpoint exception until kprobe is processed completely.

I don't think that's correct? We only really need to disable interrupts
when embarking on the single-step?

> + * Without disabling interrupt on local CPU, there is a chance of
> + * interrupt occurrence in the period of exception return and  start of
> + * out-of-line single-step, that result in wrongly single stepping
> + * the interrupt handler.
> + */
> +static void __kprobes kprobes_save_local_irqflag(struct pt_regs *regs)
> +{
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	kcb->saved_irqflag = regs->pstate;
> +	regs->pstate |= PSR_I_BIT;
> +}
> +
> +static void __kprobes kprobes_restore_local_irqflag(struct pt_regs *regs)
> +{
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	if (kcb->saved_irqflag & PSR_I_BIT)
> +		regs->pstate |= PSR_I_BIT;
> +	else
> +		regs->pstate &= ~PSR_I_BIT;
> +}
> +
> +static void __kprobes
> +set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
> +{
> +	kcb->ss_ctx.ss_status = KPROBES_STEP_PENDING;
> +	kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
> +}
> +
> +static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
> +{
> +	kcb->ss_ctx.ss_status = KPROBES_STEP_NONE;
> +	kcb->ss_ctx.match_addr = 0;
> +}
> +
> +static void __kprobes
> +skip_singlestep_missed(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
> +{
> +	/* set return addr to next pc to continue */
> +	instruction_pointer(regs) += sizeof(kprobe_opcode_t);
> +}
> +
> +static void __kprobes setup_singlestep(struct kprobe *p,
> +				       struct pt_regs *regs,
> +				       struct kprobe_ctlblk *kcb, int reenter)
> +{
> +	unsigned long slot;
> +
> +	if (reenter) {
> +		save_previous_kprobe(kcb);
> +		set_current_kprobe(p);
> +		kcb->kprobe_status = KPROBE_REENTER;
> +	} else {
> +		kcb->kprobe_status = KPROBE_HIT_SS;
> +	}
> +
> +	if (p->ainsn.insn) {
> +		/* prepare for single stepping */
> +		slot = (unsigned long)p->ainsn.insn;
> +
> +		set_ss_context(kcb, slot);	/* mark pending ss */
> +
> +		if (kcb->kprobe_status == KPROBE_REENTER)
> +			spsr_set_debug_flag(regs, 0);
> +
> +		/* IRQs and single stepping do not mix well. */
> +		kprobes_save_local_irqflag(regs);
> +		kernel_enable_single_step(regs);
> +		instruction_pointer(regs) = slot;
> +	} else	{
> +		BUG();
> +	}
> +}
> +
> +static int __kprobes reenter_kprobe(struct kprobe *p,
> +				    struct pt_regs *regs,
> +				    struct kprobe_ctlblk *kcb)
> +{
> +	switch (kcb->kprobe_status) {
> +	case KPROBE_HIT_SSDONE:
> +	case KPROBE_HIT_ACTIVE:
> +		if (!p->ainsn.check_condn || p->ainsn.check_condn(p, regs)) {
> +			kprobes_inc_nmissed_count(p);
> +			setup_singlestep(p, regs, kcb, 1);
> +		} else	{
> +			/* condition check failed, skip stepping */
> +			skip_singlestep_missed(kcb, regs);
> +		}
> +		break;
> +	case KPROBE_HIT_SS:
> +		pr_warn("Unrecoverable kprobe detected at %p.\n", p->addr);
> +		dump_kprobe(p);
> +		BUG();
> +		break;
> +	default:
> +		WARN_ON(1);
> +		return 0;
> +	}
> +
> +	return 1;
> +}
> +
> +static void __kprobes
> +post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
> +{
> +	struct kprobe *cur = kprobe_running();
> +
> +	if (!cur)
> +		return;
> +
> +	/* return addr restore if non-branching insn */
> +	if (cur->ainsn.restore.type == RESTORE_PC) {
> +		instruction_pointer(regs) = cur->ainsn.restore.addr;
> +		if (!instruction_pointer(regs))
> +			BUG();
> +	}
> +
> +	/* restore back original saved kprobe variables and continue */
> +	if (kcb->kprobe_status == KPROBE_REENTER) {
> +		restore_previous_kprobe(kcb);
> +		return;
> +	}
> +	/* call post handler */
> +	kcb->kprobe_status = KPROBE_HIT_SSDONE;
> +	if (cur->post_handler)	{
> +		/* post_handler can hit breakpoint and single step
> +		 * again, so we enable D-flag for recursive exception.
> +		 */
> +		cur->post_handler(cur, regs, 0);
> +	}
> +
> +	reset_current_kprobe();
> +}
> +
> +int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
> +{
> +	struct kprobe *cur = kprobe_running();
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	switch (kcb->kprobe_status) {
> +	case KPROBE_HIT_SS:
> +	case KPROBE_REENTER:
> +		/*
> +		 * We are here because the instruction being single
> +		 * stepped caused a page fault. We reset the current
> +		 * kprobe and the ip points back to the probe address
> +		 * and allow the page fault handler to continue as a
> +		 * normal page fault.
> +		 */
> +		instruction_pointer(regs) = (unsigned long)cur->addr;
> +		if (!instruction_pointer(regs))
> +			BUG();
> +		if (kcb->kprobe_status == KPROBE_REENTER)
> +			restore_previous_kprobe(kcb);
> +		else
> +			reset_current_kprobe();
> +
> +		break;
> +	case KPROBE_HIT_ACTIVE:
> +	case KPROBE_HIT_SSDONE:
> +		/*
> +		 * We increment the nmissed count for accounting,
> +		 * we can also use npre/npostfault count for accounting
> +		 * these specific fault cases.
> +		 */
> +		kprobes_inc_nmissed_count(cur);
> +
> +		/*
> +		 * We come here because instructions in the pre/post
> +		 * handler caused the page_fault, this could happen
> +		 * if handler tries to access user space by
> +		 * copy_from_user(), get_user() etc. Let the
> +		 * user-specified handler try to fix it first.
> +		 */
> +		if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
> +			return 1;
> +
> +		/*
> +		 * In case the user-specified fault handler returned
> +		 * zero, try to fix up.
> +		 */
> +		if (fixup_exception(regs))
> +			return 1;
> +
> +		break;
> +	}
> +	return 0;
> +}

How is kprobe_fault_handler executed?
For arch/arm I see that it's wired in via:
25ce1dd ARM kprobes: add the kprobes hook to the page fault handler

> +
> +int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
> +				       unsigned long val, void *data)
> +{
> +	return NOTIFY_DONE;
> +}
> +
> +void __kprobes kprobe_handler(struct pt_regs *regs)
> +{
> +	struct kprobe *p, *cur;
> +	struct kprobe_ctlblk *kcb;
> +	unsigned long addr = instruction_pointer(regs);
> +
> +	kcb = get_kprobe_ctlblk();
> +	cur = kprobe_running();
> +
> +	p = get_kprobe((kprobe_opcode_t *) addr);
> +
> +	if (p) {
> +		if (cur) {
> +			if (reenter_kprobe(p, regs, kcb))
> +				return;
> +		} else if (!p->ainsn.check_condn ||
> +			   p->ainsn.check_condn(p, regs)) {
> +			/* Probe hit and conditional execution check ok. */
> +			set_current_kprobe(p);
> +			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> +
> +			/*
> +			 * If we have no pre-handler or it returned 0, we
> +			 * continue with normal processing.  If we have a
> +			 * pre-handler and it returned non-zero, it prepped
> +			 * for calling the break_handler below on re-entry,
> +			 * so get out doing nothing more here.
> +			 *
> +			 * pre_handler can hit a breakpoint and can step thru
> +			 * before return, keep PSTATE D-flag enabled until
> +			 * pre_handler return back.
> +			 */
> +			if (!p->pre_handler || !p->pre_handler(p, regs)) {
> +				kcb->kprobe_status = KPROBE_HIT_SS;
> +				setup_singlestep(p, regs, kcb, 0);
> +				return;
> +			}
> +		} else {
> +			/*
> +			 * Breakpoint hit but conditional check failed,
> +			 * so just skip the instruction (NOP behaviour)
> +			 */
> +			skip_singlestep_missed(kcb, regs);
> +			return;
> +		}
> +	} else if (*(kprobe_opcode_t *) addr != BRK64_OPCODE_KPROBES) {
> +		/*
> +		 * The breakpoint instruction was removed right
> +		 * after we hit it.  Another cpu has removed
> +		 * either a probepoint or a debugger breakpoint
> +		 * at this address.  In either case, no further
> +		 * handling of this interrupt is appropriate.
> +		 * Return back to original instruction, and continue.
> +		 */
> +		return;
> +	} else if (cur) {
> +		/* We probably hit a jprobe.  Call its break handler. */
> +		if (cur->break_handler && cur->break_handler(cur, regs)) {
> +			kcb->kprobe_status = KPROBE_HIT_SS;
> +			setup_singlestep(cur, regs, kcb, 0);
> +			return;
> +		}
> +	} else {
> +		/* breakpoint is removed, now in a race
> +		 * Return back to original instruction & continue.
> +		 */
> +	}
> +}
> +
> +static int __kprobes
> +kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
> +{
> +	if ((kcb->ss_ctx.ss_status == KPROBES_STEP_PENDING)
> +	    && (kcb->ss_ctx.match_addr == addr)) {
> +		clear_ss_context(kcb);	/* clear pending ss */
> +		return DBG_HOOK_HANDLED;
> +	}
> +	/* not ours, kprobes should ignore it */
> +	return DBG_HOOK_ERROR;
> +}
> +
> +static int __kprobes
> +kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
> +{
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +	int retval;
> +
> +	/* return error if this is not our step */
> +	retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
> +
> +	if (retval == DBG_HOOK_HANDLED) {
> +		kprobes_restore_local_irqflag(regs);
> +		kernel_disable_single_step();
> +
> +		if (kcb->kprobe_status == KPROBE_REENTER)
> +			spsr_set_debug_flag(regs, 1);
> +
> +		post_kprobe_handler(kcb, regs);
> +	}
> +
> +	return retval;
> +}
> +
> +static int __kprobes
> +kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
> +{
> +	kprobe_handler(regs);
> +	return DBG_HOOK_HANDLED;
> +}
> +
> +int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
> +{
> +	struct jprobe *jp = container_of(p, struct jprobe, kp);
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +	long stack_ptr = stack_pointer(regs);
> +
> +	kcb->jprobe_saved_regs = *regs;
> +	memcpy(kcb->jprobes_stack, (void *)stack_ptr,
> +	       MIN_STACK_SIZE(stack_ptr));
> +
> +	instruction_pointer(regs) = (long)jp->entry;
> +	preempt_disable();
> +	return 1;
> +}
> +
> +void __kprobes jprobe_return(void)
> +{
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	/*
> +	 * Jprobe handler return by entering break exception,
> +	 * encoded same as kprobe, but with following conditions
> +	 * -a magic number in x0 to identify from rest of other kprobes.
> +	 * -restore stack addr to original saved pt_regs
> +	 */
> +	asm volatile ("ldr x0, [%0]\n\t"
> +		      "mov sp, x0\n\t"
> +		      "ldr x0, =" __stringify(JPROBES_MAGIC_NUM) "\n\t"
> +		      "BRK %1\n\t"
> +		      "NOP\n\t"
> +		      :
> +		      : "r"(&kcb->jprobe_saved_regs.sp),
> +		      "I"(BRK64_ESR_KPROBES)
> +		      : "memory");
> +}
> +
> +int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
> +{
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +	long stack_addr = kcb->jprobe_saved_regs.sp;
> +	long orig_sp = stack_pointer(regs);
> +	struct jprobe *jp = container_of(p, struct jprobe, kp);
> +
> +	if (regs->regs[0] == JPROBES_MAGIC_NUM) {
> +		if (orig_sp != stack_addr) {
> +			struct pt_regs *saved_regs =
> +			    (struct pt_regs *)kcb->jprobe_saved_regs.sp;
> +			pr_err("current sp %lx does not match saved sp %lx\n",
> +			       orig_sp, stack_addr);
> +			pr_err("Saved registers for jprobe %p\n", jp);
> +			show_regs(saved_regs);
> +			pr_err("Current registers\n");
> +			show_regs(regs);
> +			BUG();
> +		}
> +		*regs = kcb->jprobe_saved_regs;
> +		memcpy((void *)stack_addr, kcb->jprobes_stack,
> +		       MIN_STACK_SIZE(stack_addr));
> +		preempt_enable_no_resched();
> +		return 1;
> +	}
> +	return 0;
> +}
> +
> +/* Break Handler hook */
> +static struct break_hook kprobes_break_hook = {
> +	.esr_mask = BRK64_ESR_MASK,
> +	.esr_val = BRK64_ESR_KPROBES,
> +	.fn = kprobe_breakpoint_handler,
> +};
> +
> +/* Single Step handler hook */
> +static struct step_hook kprobes_step_hook = {
> +	.fn = kprobe_single_step_handler,
> +};
> +
> +int __init arch_init_kprobes(void)
> +{
> +	register_break_hook(&kprobes_break_hook);
> +	register_step_hook(&kprobes_step_hook);
> +
> +	return 0;
> +}
> diff --git a/arch/arm64/kernel/kprobes.h b/arch/arm64/kernel/kprobes.h
> new file mode 100644
> index 0000000..93c54b4
> --- /dev/null
> +++ b/arch/arm64/kernel/kprobes.h
> @@ -0,0 +1,30 @@
> +/*
> + * arch/arm64/kernel/kprobes.h
> + *
> + * Copyright (C) 2013 Linaro Limited.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +
> +#ifndef _ARM_KERNEL_KPROBES_H
> +#define _ARM_KERNEL_KPROBES_H
> +
> +/* BRK opcodes with ESR encoding  */
> +#define BRK64_ESR_MASK		0xFFFF
> +#define BRK64_ESR_KPROBES	0x0004
> +#define BRK64_OPCODE_KPROBES	0xD4200080	/* "brk 0x4" */
> +#define ARCH64_NOP_OPCODE	0xD503201F
> +
> +#define JPROBES_MAGIC_NUM	0xa5a5a5a5a5a5a5a5
> +
> +/* Move this out to appropriate header file */
> +int fixup_exception(struct pt_regs *regs);
> +
> +#endif /* _ARM_KERNEL_KPROBES_H */
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 9965ec8..5402a98 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -80,6 +80,7 @@ SECTIONS
>  			TEXT_TEXT
>  			SCHED_TEXT
>  			LOCK_TEXT
> +			KPROBES_TEXT
>  			HYPERVISOR_TEXT
>  			*(.fixup)
>  			*(.gnu.warning)
> -- 
> 1.8.1.2
> 

^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 5/6] arm64: Add kernel return probes support(kretprobes)
  2015-01-11  4:03 ` [PATCH v4 5/6] arm64: Add kernel return probes support(kretprobes) David Long
@ 2015-01-12 14:01   ` Steve Capper
  0 siblings, 0 replies; 21+ messages in thread
From: Steve Capper @ 2015-01-12 14:01 UTC (permalink / raw)
  To: David Long
  Cc: linux-arm-kernel, Russell King, Sandeepa Prabhu, William Cohen,
	Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

On Sat, Jan 10, 2015 at 11:03:20PM -0500, David Long wrote:
> From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
> 
> AArch64 ISA does not have instructions to pop the PC register
> value from the stack(like ARM v7 has ldmia {...,pc}) without using
> one of the general purpose registers. This means return probes
> cannot return to the actual return address directly without
> modifying register context, and without trapping into debug exception.
> 
> So, like many other architectures, we prepare a global routine
> with NOPs which serve as a trampoline to hack away the
> function return address by placing an extra kprobe on the
> trampoline entry.
> 
> The pre-handler of this special 'trampoline' kprobe executes the return
> probe handler functions and restores original return address in ELR_EL1.
> This way the saved pt_regs still hold the original register context to be
> carried back to the probed kernel function.
> 
> Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
> Signed-off-by: David A. Long <dave.long@linaro.org>
> ---
>  arch/arm64/Kconfig               |   1 +
>  arch/arm64/include/asm/kprobes.h |   1 +
>  arch/arm64/kernel/kprobes.c      | 114 ++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 115 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index b3f61ba..de4f056 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -68,6 +68,7 @@ config ARM64
>  	select HAVE_RCU_TABLE_FREE
>  	select HAVE_SYSCALL_TRACEPOINTS
>  	select HAVE_KPROBES if !XIP_KERNEL
> +	select HAVE_KRETPROBES if HAVE_KPROBES
>  	select IRQ_DOMAIN
>  	select MODULES_USE_ELF_RELA
>  	select NO_BOOTMEM
> diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
> index b35d3b9..a2de3b8 100644
> --- a/arch/arm64/include/asm/kprobes.h
> +++ b/arch/arm64/include/asm/kprobes.h
> @@ -56,5 +56,6 @@ void arch_remove_kprobe(struct kprobe *);
>  int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
>  int kprobe_exceptions_notify(struct notifier_block *self,
>  			     unsigned long val, void *data);
> +void kretprobe_trampoline(void);
>  
>  #endif /* _ARM_KPROBES_H */
> diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
> index 31a7894e..cd1069c 100644
> --- a/arch/arm64/kernel/kprobes.c
> +++ b/arch/arm64/kernel/kprobes.c
> @@ -559,6 +559,117 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
>  	return 0;
>  }
>  
> +/*
> + * Kretprobes: kernel return probes handling
> + *
> + * AArch64 mode does not support popping the PC value from the
> + * stack like on ARM 32-bit (ldmia {..,pc}), so atleast one
> + * register need to be used to achieve branching/return.
> + * It means return probes cannot return back to the original
> + * return address directly without modifying the register context.
> + *
> + * So like other architectures, we prepare a global routine
> + * with NOPs, which serve as trampoline address that hack away the
> + * function return, with the exact register context.
> + * Placing a kprobe on trampoline routine entry will trap again to
> + * execute return probe handlers and restore original return address
> + * in ELR_EL1, this way saved pt_regs still hold the original
> + * register values to be carried back to the caller.
> + */
> +static void __used kretprobe_trampoline_holder(void)
> +{
> +	asm volatile (".global kretprobe_trampoline\n"
> +			"kretprobe_trampoline:\n"
> +			"NOP\n\t"
> +			"NOP\n\t");
> +}
> +
> +static int __kprobes
> +trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
> +{
> +	struct kretprobe_instance *ri = NULL;
> +	struct hlist_head *head, empty_rp;
> +	struct hlist_node *tmp;
> +	unsigned long flags, orig_ret_addr = 0;
> +	unsigned long trampoline_address =
> +		(unsigned long)&kretprobe_trampoline;
> +
> +	INIT_HLIST_HEAD(&empty_rp);
> +	kretprobe_hash_lock(current, &head, &flags);
> +
> +	/*
> +	 * It is possible to have multiple instances associated with a given
> +	 * task either because multiple functions in the call path have
> +	 * a return probe installed on them, and/or more than one return
> +	 * probe was registered for a target function.
> +	 *
> +	 * We can handle this because:
> +	 *     - instances are always inserted at the head of the list
> +	 *     - when multiple return probes are registered for the same
> +	 *       function, the first instance's ret_addr will point to the
> +	 *       real return address, and all the rest will point to
> +	 *       kretprobe_trampoline
> +	 */
> +	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
> +		if (ri->task != current)
> +			/* another task is sharing our hash bucket */
> +			continue;
> +
> +		if (ri->rp && ri->rp->handler) {
> +			__this_cpu_write(current_kprobe, &ri->rp->kp);
> +			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
> +			ri->rp->handler(ri, regs);
> +			__this_cpu_write(current_kprobe, NULL);
> +		}
> +
> +		orig_ret_addr = (unsigned long)ri->ret_addr;
> +		recycle_rp_inst(ri, &empty_rp);
> +
> +		if (orig_ret_addr != trampoline_address)
> +			/*
> +			 * This is the real return address. Any other
> +			 * instances associated with this task are for
> +			 * other calls deeper on the call stack
> +			 */
> +			break;
> +	}
> +
> +	kretprobe_assert(ri, orig_ret_addr, trampoline_address);
> +	/* restore the original return address */
> +	instruction_pointer(regs) = orig_ret_addr;
> +	reset_current_kprobe();
> +	kretprobe_hash_unlock(current, &flags);
> +
> +	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
> +		hlist_del(&ri->hlist);
> +		kfree(ri);
> +	}
> +
> +	kprobes_restore_local_irqflag(regs);

I don't think we want this, it causes my system to crash when I do the
following:

echo "p:memcpy memcpy size=%x2" > /sys/kernel/debug/tracing/kprobe_events
echo "r:memcpyret memcpy ret=%x0" >> /sys/kernel/debug/tracing/kprobe_events
perf record -e 'kprobes:*' -a -g sleep 5

The failure mode is the familar one at:
fs/buffer.c:1257

static inline void check_irqs_on(void)
{
#ifdef irqs_disabled
        BUG_ON(irqs_disabled());
#endif
}

If I remove the line, then everything behaves for me.

> +
> +	/* return 1 so that post handlers not called */
> +	return 1;
> +}
> +
> +void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
> +				      struct pt_regs *regs)
> +{
> +	ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
> +
> +	/* replace return addr (x30) with trampoline */
> +	regs->regs[30] = (long)&kretprobe_trampoline;
> +}
> +
> +static struct kprobe trampoline = {
> +	.addr = (kprobe_opcode_t *) &kretprobe_trampoline,
> +	.pre_handler = trampoline_probe_handler
> +};
> +
> +int __kprobes arch_trampoline_kprobe(struct kprobe *p)
> +{
> +	return p->addr == (kprobe_opcode_t *) &kretprobe_trampoline;
> +}
> +
>  /* Break Handler hook */
>  static struct break_hook kprobes_break_hook = {
>  	.esr_mask = BRK64_ESR_MASK,
> @@ -576,5 +687,6 @@ int __init arch_init_kprobes(void)
>  	register_break_hook(&kprobes_break_hook);
>  	register_step_hook(&kprobes_step_hook);
>  
> -	return 0;
> +	/* register trampoline for kret probe */
> +	return register_kprobe(&trampoline);
>  }
> -- 
> 1.8.1.2
> 

^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support
  2015-01-11  4:03 [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support David Long
                   ` (5 preceding siblings ...)
  2015-01-11  4:03 ` [PATCH v4 6/6] kprobes: Add arm64 case in kprobe example module David Long
@ 2015-01-12 14:09 ` Steve Capper
  2015-01-14 11:55   ` Pratyush Anand
  6 siblings, 1 reply; 21+ messages in thread
From: Steve Capper @ 2015-01-12 14:09 UTC (permalink / raw)
  To: David Long
  Cc: linux-arm-kernel, Russell King, Sandeepa Prabhu, William Cohen,
	Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

On Sat, Jan 10, 2015 at 11:03:15PM -0500, David Long wrote:
> From: "David A. Long" <dave.long@linaro.org>
> 
> This patchset is heavily based on Sandeepa Prabhu's ARM v8 kprobes patches, first
> seen in October 2013. This version attempts to address concerns raised by
> reviewers and also fixes problems discovered during testing, particularly during
> SMP testing.
> 
> This patchset adds support for kernel probes(kprobes), jump probes(jprobes)
> and return probes(kretprobes) support for ARM64.
> 
> The kprobes mechanism makes use of software breakpoint and single stepping
> support available in the ARM v8 kernel.
> 
> Changes since v2 include:
> 
> 1) Removal of NOP padding in kprobe XOL slots. Slots are now exactly one
> instruction long.
> 2) Disabling of interrupts during execution in single-step mode.
> 3) Fixing of numerous problems in instruction simulation code (mostly
> thanks to Will Cohen).
> 4) Support for the HAVE_REGS_AND_STACK_ACCESS_API feature is added, to allow
> access to kprobes through debugfs.
> 5) kprobes is *not* enabled in defconfig.
> 6) Numerous complaints from checkpatch have been cleaned up, although a couple
> remain as removing the function pointer typedefs results in ugly code.
> 
> Changes since v3 include:
> 
> 1) Remove table-driven instruction parsing and replace with an if statement
> calling out to old and new instruction test functions in insn.c.
> 2) I removed the addition of orig_x0 to ptrace.h.
> 3) Reorder the patches.
> 4) Replace the previous interrupt disabling (from Will Cohen) with
> an improved solution (from Steve Capper).

Hi David,
I've left feedback on the patches in the series.

I ran into two major issues:
  1) trampoline_probe_handler had an errant call to:
      kprobes_restore_local_irqflag (this caused crashes for me until
      I removed it).

  2) I couldn't see how kprobe_fault_handler is called.

I've performed my memcpy tests on Juno running 3.19-rc3, and it appears
stable once trampoline_probe_handler is adjusted.

Cheers,
-- 
Steve

> 
> David A. Long (2):
>   arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature
>   arm64: Add more test functions to insn.c
> 
> Sandeepa Prabhu (4):
>   arm64: Kprobes with single stepping support
>   arm64: Kprobes instruction simulation support
>   arm64: Add kernel return probes support(kretprobes)
>   kprobes: Add arm64 case in kprobe example module
> 
>  arch/arm64/Kconfig                       |   3 +
>  arch/arm64/include/asm/insn.h            |  21 +-
>  arch/arm64/include/asm/kprobes.h         |  61 +++
>  arch/arm64/include/asm/probes.h          |  50 +++
>  arch/arm64/include/asm/ptrace.h          |  32 +-
>  arch/arm64/include/uapi/asm/ptrace.h     |  36 ++
>  arch/arm64/kernel/Makefile               |   3 +
>  arch/arm64/kernel/insn.c                 |  18 +
>  arch/arm64/kernel/kprobes-arm64.c        | 161 +++++++
>  arch/arm64/kernel/kprobes-arm64.h        |  30 ++
>  arch/arm64/kernel/kprobes.c              | 692 +++++++++++++++++++++++++++++++
>  arch/arm64/kernel/kprobes.h              |  30 ++
>  arch/arm64/kernel/probes-condn-check.c   | 122 ++++++
>  arch/arm64/kernel/probes-simulate-insn.c | 174 ++++++++
>  arch/arm64/kernel/probes-simulate-insn.h |  33 ++
>  arch/arm64/kernel/ptrace.c               | 119 ++++++
>  arch/arm64/kernel/vmlinux.lds.S          |   1 +
>  samples/kprobes/kprobe_example.c         |   8 +
>  18 files changed, 1591 insertions(+), 3 deletions(-)
>  create mode 100644 arch/arm64/include/asm/kprobes.h
>  create mode 100644 arch/arm64/include/asm/probes.h
>  create mode 100644 arch/arm64/kernel/kprobes-arm64.c
>  create mode 100644 arch/arm64/kernel/kprobes-arm64.h
>  create mode 100644 arch/arm64/kernel/kprobes.c
>  create mode 100644 arch/arm64/kernel/kprobes.h
>  create mode 100644 arch/arm64/kernel/probes-condn-check.c
>  create mode 100644 arch/arm64/kernel/probes-simulate-insn.c
>  create mode 100644 arch/arm64/kernel/probes-simulate-insn.h
> 
> -- 
> 1.8.1.2
> 

^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 3/6] arm64: Kprobes with single stepping support
  2015-01-11  4:03 ` [PATCH v4 3/6] arm64: Kprobes with single stepping support David Long
  2015-01-12 13:31   ` Steve Capper
@ 2015-01-14  9:30   ` Pratyush Anand
  2015-01-16 19:28     ` David Long
  1 sibling, 1 reply; 21+ messages in thread
From: Pratyush Anand @ 2015-01-14  9:30 UTC (permalink / raw)
  To: David Long
  Cc: linux-arm-kernel, Russell King, Sandeepa Prabhu, William Cohen,
	Steve Capper, Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel, Pratyush Anand

Hi Dave,

On Sun, Jan 11, 2015 at 9:33 AM, David Long <dave.long@linaro.org> wrote:
> From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
>
> Add support for basic kernel probes(kprobes) and jump probes
> (jprobes) for ARM64.
>
> Kprobes will utilize software breakpoint and single step debug
> exceptions supported on ARM v8.
>
> Software breakpoint is placed at the probe address to trap the
> kernel execution into kprobe handler.
>
> ARM v8 supports single stepping to be enabled while exception return
> (ERET) with next PC in exception return address (ELR_EL1). The
> kprobe handler prepares an executable memory slot for out-of-line
> execution with a copy of the original instruction being probed, and
> enables single stepping from the instruction slot. With this scheme,
> the instruction is executed with the exact same register context
> 'except PC' that points to instruction slot.
>
> Debug mask(PSTATE.D) is enabled only when single stepping a recursive
> kprobe, e.g.: during kprobes reenter so that probed instruction can be
> single stepped within the kprobe handler -exception- context.
> The recursion depth of kprobe is always 2, i.e. upon probe re-entry,
> any further re-entry is prevented by not calling handlers and the case
> counted as a missed kprobe).
>
> Single stepping from slot has a drawback on PC-relative accesses
> like branching and symbolic literals access as offset from new PC
> (slot address) may not be ensured to fit in immediate value of
> opcode. Such instructions needs simulation, so reject
> probing such instructions.
>
> Instructions generating exceptions or cpu mode change are rejected,
> and not allowed to insert probe for these instructions.
>
> Instructions using Exclusive Monitor are rejected too.
>
> System instructions are mostly enabled for stepping, except MSR
> immediate that updates "daif" flags in PSTATE, which are not safe
> for probing.
>
> Changes since v3:
> from David Long:
> 1) Removed unnecessary addtion of NOP after out-of-line instruction.
> 2) Replaced table-driven instruction parsing with calls to external
>    test functions.
> from Steve Capper:
> 3) Disable local irq while executing out of line instruction.
>
> Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
> Signed-off-by: Steve Capper <steve.capper@linaro.org>
> Signed-off-by: David A. Long <dave.long@linaro.org>
> ---
>  arch/arm64/Kconfig                |   1 +
>  arch/arm64/include/asm/kprobes.h  |  60 +++++
>  arch/arm64/include/asm/probes.h   |  50 ++++
>  arch/arm64/include/asm/ptrace.h   |   3 +-
>  arch/arm64/kernel/Makefile        |   1 +
>  arch/arm64/kernel/kprobes-arm64.c |  65 +++++
>  arch/arm64/kernel/kprobes-arm64.h |  28 ++
>  arch/arm64/kernel/kprobes.c       | 551 ++++++++++++++++++++++++++++++++++++++
>  arch/arm64/kernel/kprobes.h       |  30 +++
>  arch/arm64/kernel/vmlinux.lds.S   |   1 +
>  10 files changed, 789 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/kprobes.h
>  create mode 100644 arch/arm64/include/asm/probes.h
>  create mode 100644 arch/arm64/kernel/kprobes-arm64.c
>  create mode 100644 arch/arm64/kernel/kprobes-arm64.h
>  create mode 100644 arch/arm64/kernel/kprobes.c
>  create mode 100644 arch/arm64/kernel/kprobes.h
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 12b3fd6..b3f61ba 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -67,6 +67,7 @@ config ARM64
>         select HAVE_REGS_AND_STACK_ACCESS_API
>         select HAVE_RCU_TABLE_FREE
>         select HAVE_SYSCALL_TRACEPOINTS
> +       select HAVE_KPROBES if !XIP_KERNEL
>         select IRQ_DOMAIN
>         select MODULES_USE_ELF_RELA
>         select NO_BOOTMEM
> diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
> new file mode 100644
> index 0000000..b35d3b9
> --- /dev/null
> +++ b/arch/arm64/include/asm/kprobes.h
> @@ -0,0 +1,60 @@
> +/*
> + * arch/arm64/include/asm/kprobes.h
> + *
> + * Copyright (C) 2013 Linaro Limited
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +
> +#ifndef _ARM_KPROBES_H
> +#define _ARM_KPROBES_H
> +
> +#include <linux/types.h>
> +#include <linux/ptrace.h>
> +#include <linux/percpu.h>
> +
> +#define __ARCH_WANT_KPROBES_INSN_SLOT
> +#define MAX_INSN_SIZE                  1
> +#define MAX_STACK_SIZE                 128
> +
> +#define flush_insn_slot(p)             do { } while (0)
> +#define kretprobe_blacklist_size       0
> +
> +#include <asm/probes.h>
> +
> +struct prev_kprobe {
> +       struct kprobe *kp;
> +       unsigned int status;
> +};
> +
> +/* Single step context for kprobe */
> +struct kprobe_step_ctx {
> +#define KPROBES_STEP_NONE      0x0
> +#define KPROBES_STEP_PENDING   0x1
> +       unsigned long ss_status;
> +       unsigned long match_addr;
> +};
> +
> +/* per-cpu kprobe control block */
> +struct kprobe_ctlblk {
> +       unsigned int kprobe_status;
> +       unsigned long saved_irqflag;
> +       struct prev_kprobe prev_kprobe;
> +       struct kprobe_step_ctx ss_ctx;
> +       struct pt_regs jprobe_saved_regs;
> +       char jprobes_stack[MAX_STACK_SIZE];
> +};
> +
> +void arch_remove_kprobe(struct kprobe *);
> +int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
> +int kprobe_exceptions_notify(struct notifier_block *self,
> +                            unsigned long val, void *data);
> +
> +#endif /* _ARM_KPROBES_H */
> diff --git a/arch/arm64/include/asm/probes.h b/arch/arm64/include/asm/probes.h
> new file mode 100644
> index 0000000..9dba74d
> --- /dev/null
> +++ b/arch/arm64/include/asm/probes.h
> @@ -0,0 +1,50 @@
> +/*
> + * arch/arm64/include/asm/probes.h
> + *
> + * Copyright (C) 2013 Linaro Limited
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + */
> +#ifndef _ARM_PROBES_H
> +#define _ARM_PROBES_H
> +
> +struct kprobe;
> +struct arch_specific_insn;
> +
> +typedef u32 kprobe_opcode_t;
> +typedef unsigned long (kprobes_pstate_check_t)(unsigned long);
> +typedef unsigned long
> +(kprobes_condition_check_t)(struct kprobe *p, struct pt_regs *);

Can we make kprobes_condition_check_t as struct kprobe indepedent, so
that it is usable by uprobe as
well..

 typedef unsigned long
(kprobes_condition_check_t)(u32 opcode, struct arch_specific_insn *asi,
               struct pt_regs *);


> +typedef void
> +(kprobes_prepare_t)(struct kprobe *, struct arch_specific_insn *);

Similarly,

 typedef void
(kprobes_prepare_t)(u32 insn, struct arch_specific_insn *);

> +typedef void (kprobes_handler_t) (u32 opcode, long addr, struct pt_regs *);
> +
> +enum pc_restore_type {
> +       NO_RESTORE,
> +       RESTORE_PC,
> +};
> +

[...]

> +static bool aarch64_insn_is_steppable(u32 insn)
> +{
> +       if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
> +               if (aarch64_insn_is_branch(insn))
> +                       return false;
> +
> +               /* modification of daif creates issues */
> +               if (aarch64_insn_is_msr_daif(insn))
> +                       return false;
> +
> +               if (aarch64_insn_is_hint(insn))
> +                       return aarch64_insn_is_nop(insn);
> +
> +               return true;
> +       }
> +
> +       if (aarch64_insn_uses_literal(insn))
> +               return false;
> +
> +       if (aarch64_insn_is_exclusive(insn))
> +               return false;
> +
> +       return true;

Default true return may not be a good idea until we are sure that we
are returning false for all possible
simulation and rejection cases. In my opinion, its better to return
true only for steppable and false for
all remaining.

> +}

[...]

> +#ifndef _ARM_KERNEL_KPROBES_H
> +#define _ARM_KERNEL_KPROBES_H
> +
> +/* BRK opcodes with ESR encoding  */
> +#define BRK64_ESR_MASK         0xFFFF
> +#define BRK64_ESR_KPROBES      0x0004
> +#define BRK64_OPCODE_KPROBES   0xD4200080      /* "brk 0x4" */

As will deacon suggested, these can be moved to debug-monitor.h and
then uprobe can also add
its defines there only.

> +#define ARCH64_NOP_OPCODE      0xD503201F

It is not being used, so can be removed.

~Pratyush

^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 2/6] arm64: Add more test functions to insn.c
  2015-01-11  4:03 ` [PATCH v4 2/6] arm64: Add more test functions to insn.c David Long
@ 2015-01-14  9:32   ` Pratyush Anand
  2015-01-16 21:27     ` David Long
  0 siblings, 1 reply; 21+ messages in thread
From: Pratyush Anand @ 2015-01-14  9:32 UTC (permalink / raw)
  To: David Long
  Cc: linux-arm-kernel, Russell King, Sandeepa Prabhu, William Cohen,
	Steve Capper, Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel, Pratyush Anand

On Sun, Jan 11, 2015 at 9:33 AM, David Long <dave.long@linaro.org> wrote:
> From: "David A. Long" <dave.long@linaro.org>
>
> Certain instructions are hard to execute correctly out-of-line (as in
> kprobes).  Test functions are added to insn.[hc] to identify these.  The
> instructions include any that use PC-relative addressing, change the PC,
> or change interrupt masking. For efficiency and simplicity test
> functions are also added for small collections of related instructions.
>
> Signed-off-by: David A. Long <dave.long@linaro.org>
> ---
>  arch/arm64/include/asm/insn.h | 21 +++++++++++++++++++--
>  arch/arm64/kernel/insn.c      | 18 ++++++++++++++++++
>  2 files changed, 37 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
> index e2ff32a..466afd4 100644
> --- a/arch/arm64/include/asm/insn.h
> +++ b/arch/arm64/include/asm/insn.h
> @@ -223,8 +223,13 @@ static __always_inline bool aarch64_insn_is_##abbr(u32 code) \
>  static __always_inline u32 aarch64_insn_get_##abbr##_value(void) \
>  { return (val); }
>
> +__AARCH64_INSN_FUNCS(adr,      0x9F000000, 0x10000000)

Should n't it be
__AARCH64_INSN_FUNCS(adr_adrp,      0x1F000000, 0x10000000)

So, that it also take care about adrp

> +__AARCH64_INSN_FUNCS(prfm_lit, 0xFF000000, 0xD8000000)

[...]

>
> +bool aarch64_insn_uses_literal(u32 insn)
> +{
> +       /* ldr/ldrsw (literal), prfm */
> +
> +       return aarch64_insn_is_ldr_lit(insn) ||
> +               aarch64_insn_is_ldrsw_lit(insn) ||

also aarch64_insn_is_adr_adrp(insn) ||


> +               aarch64_insn_is_prfm_lit(insn);
> +}
> +
> +bool aarch64_insn_is_branch(u32 insn)
> +{
> +       /* b, bl, cb*, tb*, b.cond, br, blr */
> +
> +       return aarch64_insn_is_b_bl_cb_tb(insn) ||
> +               aarch64_insn_is_br_blr(insn) ||

also aarch64_insn_is_ret(insn) ||

> +               aarch64_insn_is_bcond(insn);
> +}
> +
>  /*

^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 4/6] arm64: Kprobes instruction simulation support
  2015-01-11  4:03 ` [PATCH v4 4/6] arm64: Kprobes instruction simulation support David Long
@ 2015-01-14  9:32   ` Pratyush Anand
  2015-01-16 21:34     ` David Long
  0 siblings, 1 reply; 21+ messages in thread
From: Pratyush Anand @ 2015-01-14  9:32 UTC (permalink / raw)
  To: David Long
  Cc: linux-arm-kernel, Russell King, Sandeepa Prabhu, William Cohen,
	Steve Capper, Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel, Pratyush Anand

On Sun, Jan 11, 2015 at 9:33 AM, David Long <dave.long@linaro.org> wrote:
> From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
>
> Add support for AArch64 instruction simulation in kprobes.
>
> Kprobes needs simulation of instructions that cannot be stepped
> from different memory location, e.g.: those instructions
> that uses PC-relative addressing. In simulation, the behaviour
> of the instruction is implemented using a copy of pt_regs.
>
> Following instruction catagories are simulated:
>  - All branching instructions(conditional, register, and immediate)
>  - Literal access instructions(load-literal, adr/adrp)
>
> Conditional execution is limited to branching instructions in
> ARM v8. If conditions at PSTATE do not match the condition fields
> of opcode, the instruction is effectively NOP. Kprobes considers
> this case as 'miss'.
> changes since v3:
> from David A. Long:
> 1) Fix incorrect simulate_ldrsw_literal() semantics.
> 2) Use instruction test functions instead of private parse table.
> from Will Cohen:
> 3) Remove PC adjustments when simulating an instruction.
> 4) Fix displacement calculations.
>
> Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
> Signed-off-by: William Cohen <wcohen@redhat.com>
> Signed-off-by: David A. Long <dave.long@linaro.org>
> ---

[...]

>  static bool aarch64_insn_is_steppable(u32 insn)
>  {
> @@ -60,6 +130,32 @@ arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
>          */
>         if (aarch64_insn_is_steppable(insn))
>                 return INSN_GOOD;
> +
> +       asi->prepare = prepare_none;
> +
> +       if (aarch64_insn_is_bcond(insn)) {
> +               asi->prepare = prepare_bcond;
> +               asi->handler = simulate_b_cond;
> +       } else if (aarch64_insn_is_cb(insn)) {
> +               asi->prepare = prepare_cbz_cbnz;
> +               asi->handler = simulate_cbz_cbnz;
> +       } else if (aarch64_insn_is_tb(insn)) {
> +               asi->prepare = prepare_tbz_tbnz;
> +               asi->handler = simulate_tbz_tbnz;
> +       } else if (aarch64_insn_is_adr(insn))

aarch64_insn_is_adr should be modified to aarch64_insn_is_adr_adrp

> +               asi->handler = simulate_adr_adrp;
> +       else if (aarch64_insn_is_b_bl(insn))
> +               asi->handler = simulate_b_bl;
> +       else if (aarch64_insn_is_ldr_lit(insn))
> +               asi->handler = simulate_ldr_literal;
> +       else if (aarch64_insn_is_ldrsw_lit(insn))
> +               asi->handler = simulate_ldrsw_literal;

also

else if (aarch64_insn_is_br_blr(insn) || aarch64_insn_is_ret(insn))
               asi->handler = simulate_br_blr_ret;


~Pratyush

^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support
  2015-01-12 14:09 ` [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support Steve Capper
@ 2015-01-14 11:55   ` Pratyush Anand
  0 siblings, 0 replies; 21+ messages in thread
From: Pratyush Anand @ 2015-01-14 11:55 UTC (permalink / raw)
  To: Steve Capper
  Cc: David Long, linux-arm-kernel, Russell King, Sandeepa Prabhu,
	William Cohen, Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel

On Mon, Jan 12, 2015 at 7:39 PM, Steve Capper <steve.capper@linaro.org> wrote:
> On Sat, Jan 10, 2015 at 11:03:15PM -0500, David Long wrote:
>> From: "David A. Long" <dave.long@linaro.org>
>>
>> This patchset is heavily based on Sandeepa Prabhu's ARM v8 kprobes patches, first
>> seen in October 2013. This version attempts to address concerns raised by
>> reviewers and also fixes problems discovered during testing, particularly during
>> SMP testing.
>>
>> This patchset adds support for kernel probes(kprobes), jump probes(jprobes)
>> and return probes(kretprobes) support for ARM64.
>>
>> The kprobes mechanism makes use of software breakpoint and single stepping
>> support available in the ARM v8 kernel.
>>
>> Changes since v2 include:
>>
>> 1) Removal of NOP padding in kprobe XOL slots. Slots are now exactly one
>> instruction long.
>> 2) Disabling of interrupts during execution in single-step mode.
>> 3) Fixing of numerous problems in instruction simulation code (mostly
>> thanks to Will Cohen).
>> 4) Support for the HAVE_REGS_AND_STACK_ACCESS_API feature is added, to allow
>> access to kprobes through debugfs.
>> 5) kprobes is *not* enabled in defconfig.
>> 6) Numerous complaints from checkpatch have been cleaned up, although a couple
>> remain as removing the function pointer typedefs results in ugly code.
>>
>> Changes since v3 include:
>>
>> 1) Remove table-driven instruction parsing and replace with an if statement
>> calling out to old and new instruction test functions in insn.c.
>> 2) I removed the addition of orig_x0 to ptrace.h.
>> 3) Reorder the patches.
>> 4) Replace the previous interrupt disabling (from Will Cohen) with
>> an improved solution (from Steve Capper).
>

Hi David,

If  you plan your next revision, may be  you can pick and squash
following patches from my tree
(https://github.com/pratyushanand/linux.git :
ml_arm64_uprobe_devel_v2_over_kprobe_v4)

abb0b22be54c ARM64: Move BRK opcodes defines from kprobes.h to debug-monitors.h
c82c2abaf751 ARM64: kprobe: Make prepare and handler function struct
kprobe independent
d95c226226dc ARM64: Remove definition of ARCH64_NOP_OPCODE
e5f3310a21c4 ARM64: kprobe: Fix few instruction which is to be simulated

~Pratyush

^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 1/6] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature
  2015-01-12 12:51   ` Steve Capper
@ 2015-01-15  7:07     ` Masami Hiramatsu
  0 siblings, 0 replies; 21+ messages in thread
From: Masami Hiramatsu @ 2015-01-15  7:07 UTC (permalink / raw)
  To: Steve Capper
  Cc: David Long, linux-arm-kernel, Russell King, Sandeepa Prabhu,
	William Cohen, Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Ananth N Mavinakayanahalli, Anil S Keshavamurthy, davem,
	linux-kernel

(2015/01/12 21:51), Steve Capper wrote:
> On Sat, Jan 10, 2015 at 11:03:16PM -0500, David Long wrote:
>> From: "David A. Long" <dave.long@linaro.org>
>>
>> Add HAVE_REGS_AND_STACK_ACCESS_API feature for arm64.
>>
>> Signed-off-by: David A. Long <dave.long@linaro.org>
>> ---
>>  arch/arm64/Kconfig                   |   1 +
>>  arch/arm64/include/asm/ptrace.h      |  29 +++++++++
>>  arch/arm64/include/uapi/asm/ptrace.h |  36 +++++++++++
>>  arch/arm64/kernel/ptrace.c           | 119 +++++++++++++++++++++++++++++++++++
>>  4 files changed, 185 insertions(+)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index b1f9a20..12b3fd6 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -64,6 +64,7 @@ config ARM64
>>  	select HAVE_PERF_EVENTS
>>  	select HAVE_PERF_REGS
>>  	select HAVE_PERF_USER_STACK_DUMP
>> +	select HAVE_REGS_AND_STACK_ACCESS_API
>>  	select HAVE_RCU_TABLE_FREE
>>  	select HAVE_SYSCALL_TRACEPOINTS
>>  	select IRQ_DOMAIN
>> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
>> index 41ed9e1..3613e49 100644
>> --- a/arch/arm64/include/asm/ptrace.h
>> +++ b/arch/arm64/include/asm/ptrace.h
>> @@ -111,6 +111,8 @@ struct pt_regs {
>>  	u64 syscallno;
>>  };
>>  
>> +#define MAX_REG_OFFSET (sizeof(struct user_pt_regs) - sizeof(u64))
>> +
>>  #define arch_has_single_step()	(1)
>>  
>>  #ifdef CONFIG_COMPAT
>> @@ -139,11 +141,38 @@ struct pt_regs {
>>  #define user_stack_pointer(regs) \
>>  	(!compat_user_mode(regs) ? (regs)->sp : (regs)->compat_sp)
>>  
>> +/**
>> + * regs_get_register() - get register value from its offset
>> + * @regs:	   pt_regs from which register value is gotten
>> + * @offset:    offset number of the register.
>> + *
>> + * regs_get_register returns the value of a register whose offset from @regs.
>> + * The @offset is the offset of the register in struct pt_regs.
>> + * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
>> + */
>> +static inline u64 regs_get_register(struct pt_regs *regs,
>> +					      unsigned int offset)
>> +{
>> +	if (unlikely(offset > MAX_REG_OFFSET))
>> +		return 0;
>> +	return *(u64 *)((u64)regs + offset);
>> +}
>> +
>> +/* Valid only for Kernel mode traps. */
>> +static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
>> +{
>> +	return regs->ARM_sp;
>> +}
>> +
>>  static inline unsigned long regs_return_value(struct pt_regs *regs)
>>  {
>>  	return regs->regs[0];
>>  }
>>  
>> +extern int regs_query_register_offset(const char *name);
>> +extern unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
>> +					       unsigned int n);
>> +
>>  /*
>>   * Are the current registers suitable for user mode? (used to maintain
>>   * security in signal handlers)
>> diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
>> index 6913643..700d28b 100644
>> --- a/arch/arm64/include/uapi/asm/ptrace.h
>> +++ b/arch/arm64/include/uapi/asm/ptrace.h
>> @@ -61,6 +61,42 @@
>>  
>>  #ifndef __ASSEMBLY__
>>  
>> +#define ARM_cpsr	pstate
>> +#define ARM_pc		pc
>> +#define ARM_sp		sp
>> +#define ARM_lr		regs[30]
>> +#define ARM_fp		regs[29]
>> +#define ARM_x28		regs[28]
>> +#define ARM_x27		regs[27]
>> +#define ARM_x26		regs[26]
>> +#define ARM_x25		regs[25]
>> +#define ARM_x24		regs[24]
>> +#define ARM_x23		regs[23]
>> +#define ARM_x22		regs[22]
>> +#define ARM_x21		regs[21]
>> +#define ARM_x20		regs[20]
>> +#define ARM_x19		regs[19]
>> +#define ARM_x18		regs[18]
>> +#define ARM_ip1		regs[17]
>> +#define ARM_ip0		regs[16]
>> +#define ARM_x15		regs[15]
>> +#define ARM_x14		regs[14]
>> +#define ARM_x13		regs[13]
>> +#define ARM_x12		regs[12]
>> +#define ARM_x11		regs[11]
>> +#define ARM_x10		regs[10]
>> +#define ARM_x9		regs[9]
>> +#define ARM_x8		regs[8]
>> +#define ARM_x7		regs[7]
>> +#define ARM_x6		regs[6]
>> +#define ARM_x5		regs[5]
>> +#define ARM_x4		regs[4]
>> +#define ARM_x3		regs[3]
>> +#define ARM_x2		regs[2]
>> +#define ARM_x1		regs[1]
>> +#define ARM_x0		regs[0]
>> +#define ARM_ORIG_x0	orig_x0
>> +
>>  /*
>>   * User structures for general purpose, floating point and debug registers.
>>   */
>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>> index d882b83..9115b25 100644
>> --- a/arch/arm64/kernel/ptrace.c
>> +++ b/arch/arm64/kernel/ptrace.c
>> @@ -48,6 +48,125 @@
>>  #define CREATE_TRACE_POINTS
>>  #include <trace/events/syscalls.h>
>>  
>> +struct pt_regs_offset {
>> +	const char *name;
>> +	int offset;
>> +};
>> +
>> +#define REG_OFFSET_NAME(r) \
>> +	{.name = #r, .offset = offsetof(struct pt_regs, ARM_##r)}
>> +#define REG_OFFSET_END {.name = NULL, .offset = 0}
>> +
>> +static const struct pt_regs_offset regoffset_table[] = {
>> +	REG_OFFSET_NAME(x0),
>> +	REG_OFFSET_NAME(x1),
>> +	REG_OFFSET_NAME(x2),
>> +	REG_OFFSET_NAME(x3),
>> +	REG_OFFSET_NAME(x4),
>> +	REG_OFFSET_NAME(x5),
>> +	REG_OFFSET_NAME(x6),
>> +	REG_OFFSET_NAME(x7),
>> +	REG_OFFSET_NAME(x8),
>> +	REG_OFFSET_NAME(x9),
>> +	REG_OFFSET_NAME(x10),
>> +	REG_OFFSET_NAME(x11),
>> +	REG_OFFSET_NAME(x12),
>> +	REG_OFFSET_NAME(x13),
>> +	REG_OFFSET_NAME(x14),
>> +	REG_OFFSET_NAME(x15),
>> +	REG_OFFSET_NAME(ip0),
>> +	REG_OFFSET_NAME(ip1),
>> +	REG_OFFSET_NAME(x18),
>> +	REG_OFFSET_NAME(x19),
>> +	REG_OFFSET_NAME(x20),
>> +	REG_OFFSET_NAME(x21),
>> +	REG_OFFSET_NAME(x22),
>> +	REG_OFFSET_NAME(x23),
>> +	REG_OFFSET_NAME(x24),
>> +	REG_OFFSET_NAME(x25),
>> +	REG_OFFSET_NAME(x26),
>> +	REG_OFFSET_NAME(x27),
>> +	REG_OFFSET_NAME(x28),
>> +	REG_OFFSET_NAME(fp),
>> +	REG_OFFSET_NAME(lr),
>> +/*
>> +	REG_OFFSET_NAME(ip),
>> +*/
> 
> Should this comment block be removed?

Agreed, I think it should be removed.
Except that, this looks good to me.

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

Thanks!

> 
>> +	REG_OFFSET_NAME(sp),
>> +	REG_OFFSET_NAME(pc),
>> +	REG_OFFSET_NAME(cpsr),
>> +	REG_OFFSET_NAME(ORIG_x0),
>> +	REG_OFFSET_END,
>> +};
>> +
>> +/**
>> + * regs_query_register_offset() - query register offset from its name
>> + * @name:	the name of a register
>> + *
>> + * regs_query_register_offset() returns the offset of a register in struct
>> + * pt_regs from its name. If the name is invalid, this returns -EINVAL;
>> + */
>> +int regs_query_register_offset(const char *name)
>> +{
>> +	const struct pt_regs_offset *roff;
>> +
>> +	for (roff = regoffset_table; roff->name != NULL; roff++)
>> +		if (!strcmp(roff->name, name))
>> +			return roff->offset;
>> +	return -EINVAL;
>> +}
>> +
>> +/**
>> + * regs_query_register_name() - query register name from its offset
>> + * @offset:	the offset of a register in struct pt_regs.
>> + *
>> + * regs_query_register_name() returns the name of a register from its
>> + * offset in struct pt_regs. If the @offset is invalid, this returns NULL;
>> + */
>> +const char *regs_query_register_name(unsigned int offset)
>> +{
>> +	const struct pt_regs_offset *roff;
>> +
>> +	for (roff = regoffset_table; roff->name != NULL; roff++)
>> +		if (roff->offset == offset)
>> +			return roff->name;
>> +	return NULL;
>> +}
>> +
>> +/**
>> + * regs_within_kernel_stack() - check the address in the stack
>> + * @regs:      pt_regs which contains kernel stack pointer.
>> + * @addr:      address which is checked.
>> + *
>> + * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
>> + * If @addr is within the kernel stack, it returns true. If not, returns false.
>> + */
>> +bool regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
>> +{
>> +	return ((addr & ~(THREAD_SIZE - 1))  ==
>> +		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1)));
>> +}
>> +
>> +/**
>> + * regs_get_kernel_stack_nth() - get Nth entry of the stack
>> + * @regs:	pt_regs which contains kernel stack pointer.
>> + * @n:		stack entry number.
>> + *
>> + * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
>> + * is specified by @regs. If the @n th entry is NOT in the kernel stack,
>> + * this returns 0.
>> + */
>> +unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
>> +{
>> +	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
>> +
>> +	addr += n;
>> +	if (regs_within_kernel_stack(regs, (unsigned long)addr))
>> +		return *addr;
>> +	else
>> +		return 0;
>> +}
>> +
>>  /*
>>   * TODO: does not yet catch signals sent when the child dies.
>>   * in exit.c or in signal.c.
>> -- 
>> 1.8.1.2
>>
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com



^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 3/6] arm64: Kprobes with single stepping support
  2015-01-14  9:30   ` Pratyush Anand
@ 2015-01-16 19:28     ` David Long
  2015-01-19  9:03       ` Pratyush Anand
  0 siblings, 1 reply; 21+ messages in thread
From: David Long @ 2015-01-16 19:28 UTC (permalink / raw)
  To: Pratyush Anand
  Cc: linux-arm-kernel, Russell King, Sandeepa Prabhu, William Cohen,
	Steve Capper, Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel, Pratyush Anand

On 01/14/15 04:30, Pratyush Anand wrote:
> Hi Dave,
>
> On Sun, Jan 11, 2015 at 9:33 AM, David Long <dave.long@linaro.org> wrote:
>> From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
>>
>> Add support for basic kernel probes(kprobes) and jump probes
>> (jprobes) for ARM64.
>>
>> Kprobes will utilize software breakpoint and single step debug
>> exceptions supported on ARM v8.
>>
>> Software breakpoint is placed at the probe address to trap the
>> kernel execution into kprobe handler.
>>
>> ARM v8 supports single stepping to be enabled while exception return
>> (ERET) with next PC in exception return address (ELR_EL1). The
>> kprobe handler prepares an executable memory slot for out-of-line
>> execution with a copy of the original instruction being probed, and
>> enables single stepping from the instruction slot. With this scheme,
>> the instruction is executed with the exact same register context
>> 'except PC' that points to instruction slot.
>>
>> Debug mask(PSTATE.D) is enabled only when single stepping a recursive
>> kprobe, e.g.: during kprobes reenter so that probed instruction can be
>> single stepped within the kprobe handler -exception- context.
>> The recursion depth of kprobe is always 2, i.e. upon probe re-entry,
>> any further re-entry is prevented by not calling handlers and the case
>> counted as a missed kprobe).
>>
>> Single stepping from slot has a drawback on PC-relative accesses
>> like branching and symbolic literals access as offset from new PC
>> (slot address) may not be ensured to fit in immediate value of
>> opcode. Such instructions needs simulation, so reject
>> probing such instructions.
>>
>> Instructions generating exceptions or cpu mode change are rejected,
>> and not allowed to insert probe for these instructions.
>>
>> Instructions using Exclusive Monitor are rejected too.
>>
>> System instructions are mostly enabled for stepping, except MSR
>> immediate that updates "daif" flags in PSTATE, which are not safe
>> for probing.
>>
>> Changes since v3:
>> from David Long:
>> 1) Removed unnecessary addtion of NOP after out-of-line instruction.
>> 2) Replaced table-driven instruction parsing with calls to external
>>     test functions.
>> from Steve Capper:
>> 3) Disable local irq while executing out of line instruction.
>>
>> Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
>> Signed-off-by: Steve Capper <steve.capper@linaro.org>
>> Signed-off-by: David A. Long <dave.long@linaro.org>
>> ---
>>   arch/arm64/Kconfig                |   1 +
>>   arch/arm64/include/asm/kprobes.h  |  60 +++++
>>   arch/arm64/include/asm/probes.h   |  50 ++++
>>   arch/arm64/include/asm/ptrace.h   |   3 +-
>>   arch/arm64/kernel/Makefile        |   1 +
>>   arch/arm64/kernel/kprobes-arm64.c |  65 +++++
>>   arch/arm64/kernel/kprobes-arm64.h |  28 ++
>>   arch/arm64/kernel/kprobes.c       | 551 ++++++++++++++++++++++++++++++++++++++
>>   arch/arm64/kernel/kprobes.h       |  30 +++
>>   arch/arm64/kernel/vmlinux.lds.S   |   1 +
>>   10 files changed, 789 insertions(+), 1 deletion(-)
>>   create mode 100644 arch/arm64/include/asm/kprobes.h
>>   create mode 100644 arch/arm64/include/asm/probes.h
>>   create mode 100644 arch/arm64/kernel/kprobes-arm64.c
>>   create mode 100644 arch/arm64/kernel/kprobes-arm64.h
>>   create mode 100644 arch/arm64/kernel/kprobes.c
>>   create mode 100644 arch/arm64/kernel/kprobes.h
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 12b3fd6..b3f61ba 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -67,6 +67,7 @@ config ARM64
>>          select HAVE_REGS_AND_STACK_ACCESS_API
>>          select HAVE_RCU_TABLE_FREE
>>          select HAVE_SYSCALL_TRACEPOINTS
>> +       select HAVE_KPROBES if !XIP_KERNEL
>>          select IRQ_DOMAIN
>>          select MODULES_USE_ELF_RELA
>>          select NO_BOOTMEM
>> diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
>> new file mode 100644
>> index 0000000..b35d3b9
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/kprobes.h
>> @@ -0,0 +1,60 @@
>> +/*
>> + * arch/arm64/include/asm/kprobes.h
>> + *
>> + * Copyright (C) 2013 Linaro Limited
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * General Public License for more details.
>> + */
>> +
>> +#ifndef _ARM_KPROBES_H
>> +#define _ARM_KPROBES_H
>> +
>> +#include <linux/types.h>
>> +#include <linux/ptrace.h>
>> +#include <linux/percpu.h>
>> +
>> +#define __ARCH_WANT_KPROBES_INSN_SLOT
>> +#define MAX_INSN_SIZE                  1
>> +#define MAX_STACK_SIZE                 128
>> +
>> +#define flush_insn_slot(p)             do { } while (0)
>> +#define kretprobe_blacklist_size       0
>> +
>> +#include <asm/probes.h>
>> +
>> +struct prev_kprobe {
>> +       struct kprobe *kp;
>> +       unsigned int status;
>> +};
>> +
>> +/* Single step context for kprobe */
>> +struct kprobe_step_ctx {
>> +#define KPROBES_STEP_NONE      0x0
>> +#define KPROBES_STEP_PENDING   0x1
>> +       unsigned long ss_status;
>> +       unsigned long match_addr;
>> +};
>> +
>> +/* per-cpu kprobe control block */
>> +struct kprobe_ctlblk {
>> +       unsigned int kprobe_status;
>> +       unsigned long saved_irqflag;
>> +       struct prev_kprobe prev_kprobe;
>> +       struct kprobe_step_ctx ss_ctx;
>> +       struct pt_regs jprobe_saved_regs;
>> +       char jprobes_stack[MAX_STACK_SIZE];
>> +};
>> +
>> +void arch_remove_kprobe(struct kprobe *);
>> +int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
>> +int kprobe_exceptions_notify(struct notifier_block *self,
>> +                            unsigned long val, void *data);
>> +
>> +#endif /* _ARM_KPROBES_H */
>> diff --git a/arch/arm64/include/asm/probes.h b/arch/arm64/include/asm/probes.h
>> new file mode 100644
>> index 0000000..9dba74d
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/probes.h
>> @@ -0,0 +1,50 @@
>> +/*
>> + * arch/arm64/include/asm/probes.h
>> + *
>> + * Copyright (C) 2013 Linaro Limited
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * General Public License for more details.
>> + */
>> +#ifndef _ARM_PROBES_H
>> +#define _ARM_PROBES_H
>> +
>> +struct kprobe;
>> +struct arch_specific_insn;
>> +
>> +typedef u32 kprobe_opcode_t;
>> +typedef unsigned long (kprobes_pstate_check_t)(unsigned long);
>> +typedef unsigned long
>> +(kprobes_condition_check_t)(struct kprobe *p, struct pt_regs *);
>
> Can we make kprobes_condition_check_t as struct kprobe indepedent, so
> that it is usable by uprobe as
> well..
>
>   typedef unsigned long
> (kprobes_condition_check_t)(u32 opcode, struct arch_specific_insn *asi,
>                 struct pt_regs *);
>

We can.  I had intended that to happen with the uprobes patch, but we 
can do that up front.

>> +typedef void
>> +(kprobes_prepare_t)(struct kprobe *, struct arch_specific_insn *);
>
> Similarly,
>
>   typedef void
> (kprobes_prepare_t)(u32 insn, struct arch_specific_insn *);
>

Yes.

>> +typedef void (kprobes_handler_t) (u32 opcode, long addr, struct pt_regs *);
>> +
>> +enum pc_restore_type {
>> +       NO_RESTORE,
>> +       RESTORE_PC,
>> +};
>> +
>
> [...]
>
>> +static bool aarch64_insn_is_steppable(u32 insn)
>> +{
>> +       if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
>> +               if (aarch64_insn_is_branch(insn))
>> +                       return false;
>> +
>> +               /* modification of daif creates issues */
>> +               if (aarch64_insn_is_msr_daif(insn))
>> +                       return false;
>> +
>> +               if (aarch64_insn_is_hint(insn))
>> +                       return aarch64_insn_is_nop(insn);
>> +
>> +               return true;
>> +       }
>> +
>> +       if (aarch64_insn_uses_literal(insn))
>> +               return false;
>> +
>> +       if (aarch64_insn_is_exclusive(insn))
>> +               return false;
>> +
>> +       return true;
>
> Default true return may not be a good idea until we are sure that we
> are returning false for all possible
> simulation and rejection cases. In my opinion, its better to return
> true only for steppable and false for
> all remaining.
>

I struggled a little with this when I did it but I decided if the 
question was:  "should we have to recognize every instruction before 
deciding it was single-steppable or should we only recognize 
instructions that are *not* single-steppable", maybe it was OK to do the 
latter while recognizing extensions to the instruction set *could* end 
up (temporarly) allowing us to try and fail (badly) at single-stepping 
any problematic new instructions.  Certainly opinions could differ.  If 
the consensus is that we can't allow this to ever happen (because old 
kprobe code is running on new hardware) then I think the only choice is 
to return to parsing binary tables.  Hopefully I could still find a way 
to leverage insn.c in that case.

>> +}
>
> [...]
>
>> +#ifndef _ARM_KERNEL_KPROBES_H
>> +#define _ARM_KERNEL_KPROBES_H
>> +
>> +/* BRK opcodes with ESR encoding  */
>> +#define BRK64_ESR_MASK         0xFFFF
>> +#define BRK64_ESR_KPROBES      0x0004
>> +#define BRK64_OPCODE_KPROBES   0xD4200080      /* "brk 0x4" */
>
> As will deacon suggested, these can be moved to debug-monitor.h and
> then uprobe can also add
> its defines there only.
>

Not seeing an earlier email about this that I've been copied on, but it 
makes sense.

>> +#define ARCH64_NOP_OPCODE      0xD503201F
>
> It is not being used, so can be removed.
>

A leftover from the previous patchset.  I'll remove it, assuming it 
doesn't become needed again in v5.

> ~Pratyush
>

-dl


^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 2/6] arm64: Add more test functions to insn.c
  2015-01-14  9:32   ` Pratyush Anand
@ 2015-01-16 21:27     ` David Long
  0 siblings, 0 replies; 21+ messages in thread
From: David Long @ 2015-01-16 21:27 UTC (permalink / raw)
  To: Pratyush Anand
  Cc: linux-arm-kernel, Russell King, Sandeepa Prabhu, William Cohen,
	Steve Capper, Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel, Pratyush Anand

On 01/14/15 04:32, Pratyush Anand wrote:
> On Sun, Jan 11, 2015 at 9:33 AM, David Long <dave.long@linaro.org> wrote:
>> From: "David A. Long" <dave.long@linaro.org>
>>
>> Certain instructions are hard to execute correctly out-of-line (as in
>> kprobes).  Test functions are added to insn.[hc] to identify these.  The
>> instructions include any that use PC-relative addressing, change the PC,
>> or change interrupt masking. For efficiency and simplicity test
>> functions are also added for small collections of related instructions.
>>
>> Signed-off-by: David A. Long <dave.long@linaro.org>
>> ---
>>   arch/arm64/include/asm/insn.h | 21 +++++++++++++++++++--
>>   arch/arm64/kernel/insn.c      | 18 ++++++++++++++++++
>>   2 files changed, 37 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
>> index e2ff32a..466afd4 100644
>> --- a/arch/arm64/include/asm/insn.h
>> +++ b/arch/arm64/include/asm/insn.h
>> @@ -223,8 +223,13 @@ static __always_inline bool aarch64_insn_is_##abbr(u32 code) \
>>   static __always_inline u32 aarch64_insn_get_##abbr##_value(void) \
>>   { return (val); }
>>
>> +__AARCH64_INSN_FUNCS(adr,      0x9F000000, 0x10000000)
>
> Should n't it be
> __AARCH64_INSN_FUNCS(adr_adrp,      0x1F000000, 0x10000000)
>
> So, that it also take care about adrp

Yes, that does look like a mistake.

>> +__AARCH64_INSN_FUNCS(prfm_lit, 0xFF000000, 0xD8000000)
>
> [...]
>
>>
>> +bool aarch64_insn_uses_literal(u32 insn)
>> +{
>> +       /* ldr/ldrsw (literal), prfm */
>> +
>> +       return aarch64_insn_is_ldr_lit(insn) ||
>> +               aarch64_insn_is_ldrsw_lit(insn) ||
>
> also aarch64_insn_is_adr_adrp(insn) ||
>

Yup.

>> +               aarch64_insn_is_prfm_lit(insn);
>> +}
>> +
>> +bool aarch64_insn_is_branch(u32 insn)
>> +{
>> +       /* b, bl, cb*, tb*, b.cond, br, blr */
>> +
>> +       return aarch64_insn_is_b_bl_cb_tb(insn) ||
>> +               aarch64_insn_is_br_blr(insn) ||
>
> also aarch64_insn_is_ret(insn) ||

The goal was to catch intructions that use a PC-relative branch, since 
the PC will not be what is expected.  Of course any instruction that 
changes the PC will have a problem too because the PC will be rewritten 
after the probe is completed.  So, yeah, this needs to be fixed.

>> +               aarch64_insn_is_bcond(insn);
>> +}
>> +
>>   /*

-dl


^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 4/6] arm64: Kprobes instruction simulation support
  2015-01-14  9:32   ` Pratyush Anand
@ 2015-01-16 21:34     ` David Long
  0 siblings, 0 replies; 21+ messages in thread
From: David Long @ 2015-01-16 21:34 UTC (permalink / raw)
  To: Pratyush Anand
  Cc: linux-arm-kernel, Russell King, Sandeepa Prabhu, William Cohen,
	Steve Capper, Catalin Marinas, Will Deacon, Jon Medhurst (Tixy),
	Masami Hiramatsu, Ananth N Mavinakayanahalli,
	Anil S Keshavamurthy, davem, linux-kernel, Pratyush Anand

On 01/14/15 04:32, Pratyush Anand wrote:
> On Sun, Jan 11, 2015 at 9:33 AM, David Long <dave.long@linaro.org> wrote:
>> From: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
>>
>> Add support for AArch64 instruction simulation in kprobes.
>>
>> Kprobes needs simulation of instructions that cannot be stepped
>> from different memory location, e.g.: those instructions
>> that uses PC-relative addressing. In simulation, the behaviour
>> of the instruction is implemented using a copy of pt_regs.
>>
>> Following instruction catagories are simulated:
>>   - All branching instructions(conditional, register, and immediate)
>>   - Literal access instructions(load-literal, adr/adrp)
>>
>> Conditional execution is limited to branching instructions in
>> ARM v8. If conditions at PSTATE do not match the condition fields
>> of opcode, the instruction is effectively NOP. Kprobes considers
>> this case as 'miss'.
>> changes since v3:
>> from David A. Long:
>> 1) Fix incorrect simulate_ldrsw_literal() semantics.
>> 2) Use instruction test functions instead of private parse table.
>> from Will Cohen:
>> 3) Remove PC adjustments when simulating an instruction.
>> 4) Fix displacement calculations.
>>
>> Signed-off-by: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
>> Signed-off-by: William Cohen <wcohen@redhat.com>
>> Signed-off-by: David A. Long <dave.long@linaro.org>
>> ---
>
> [...]
>
>>   static bool aarch64_insn_is_steppable(u32 insn)
>>   {
>> @@ -60,6 +130,32 @@ arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
>>           */
>>          if (aarch64_insn_is_steppable(insn))
>>                  return INSN_GOOD;
>> +
>> +       asi->prepare = prepare_none;
>> +
>> +       if (aarch64_insn_is_bcond(insn)) {
>> +               asi->prepare = prepare_bcond;
>> +               asi->handler = simulate_b_cond;
>> +       } else if (aarch64_insn_is_cb(insn)) {
>> +               asi->prepare = prepare_cbz_cbnz;
>> +               asi->handler = simulate_cbz_cbnz;
>> +       } else if (aarch64_insn_is_tb(insn)) {
>> +               asi->prepare = prepare_tbz_tbnz;
>> +               asi->handler = simulate_tbz_tbnz;
>> +       } else if (aarch64_insn_is_adr(insn))
>
> aarch64_insn_is_adr should be modified to aarch64_insn_is_adr_adrp

Yes.

>> +               asi->handler = simulate_adr_adrp;
>> +       else if (aarch64_insn_is_b_bl(insn))
>> +               asi->handler = simulate_b_bl;
>> +       else if (aarch64_insn_is_ldr_lit(insn))
>> +               asi->handler = simulate_ldr_literal;
>> +       else if (aarch64_insn_is_ldrsw_lit(insn))
>> +               asi->handler = simulate_ldrsw_literal;
>
> also
>
> else if (aarch64_insn_is_br_blr(insn) || aarch64_insn_is_ret(insn))
>                 asi->handler = simulate_br_blr_ret;

Yes.

>
> ~Pratyush
>

-dl


^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 3/6] arm64: Kprobes with single stepping support
  2015-01-16 19:28     ` David Long
@ 2015-01-19  9:03       ` Pratyush Anand
  2015-01-21 18:02         ` David Long
  0 siblings, 1 reply; 21+ messages in thread
From: Pratyush Anand @ 2015-01-19  9:03 UTC (permalink / raw)
  To: David Long, Pratyush Anand
  Cc: Jon Medhurst (Tixy),
	Steve Capper, Ananth N Mavinakayanahalli, Sandeepa Prabhu,
	Catalin Marinas, Will Deacon, linux-kernel, Anil S Keshavamurthy,
	Masami Hiramatsu, Russell King, William Cohen, davem,
	linux-arm-kernel, oleg Nesterov



On Saturday 17 January 2015 12:58 AM, David Long wrote:
>>> +static bool aarch64_insn_is_steppable(u32 insn)
>>> +{
>>> +       if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
>>> +               if (aarch64_insn_is_branch(insn))
>>> +                       return false;
>>> +
>>> +               /* modification of daif creates issues */
>>> +               if (aarch64_insn_is_msr_daif(insn))
>>> +                       return false;
>>> +
>>> +               if (aarch64_insn_is_hint(insn))
>>> +                       return aarch64_insn_is_nop(insn);
>>> +
>>> +               return true;
>>> +       }
>>> +
>>> +       if (aarch64_insn_uses_literal(insn))
>>> +               return false;
>>> +
>>> +       if (aarch64_insn_is_exclusive(insn))
>>> +               return false;
>>> +
>>> +       return true;
>>
>> Default true return may not be a good idea until we are sure that we
>> are returning false for all possible
>> simulation and rejection cases. In my opinion, its better to return
>> true only for steppable and false for
>> all remaining.
>>
>
> I struggled a little with this when I did it but I decided if the
> question was:  "should we have to recognize every instruction before
> deciding it was single-steppable or should we only recognize
> instructions that are *not* single-steppable", maybe it was OK to do the
> latter while recognizing extensions to the instruction set *could* end
> up (temporarly) allowing us to try and fail (badly) at single-stepping
> any problematic new instructions.  Certainly opinions could differ.  If

Lets see what others say, but I see that this approach will result in 
undesired behavior. For example: a probe has been tried to insert to svc 
instruction. SVC or any other exception generation instruction is 
expected to be rejected. But, current aarch64_insn_is_steppable will 
return true for it and then kprobe/uprobe code will allow to insert 
probe at that instruction, which will be wrong, no? I mean, I do not see 
a way to get into last else (INSN_REJECTED) of arm_kprobe_decode_insn.

So, if we go with this approach we need to insure that we cover all 
simulation-able and reject-able cases in aarch64_insn_is_steppable.

~Pratyush



> the consensus is that we can't allow this to ever happen (because old
> kprobe code is running on new hardware) then I think the only choice is
> to return to parsing binary tables.  Hopefully I could still find a way
> to leverage insn.c in that case.

^ permalink raw reply	[flat|nested] 21+ messages in thread

* Re: [PATCH v4 3/6] arm64: Kprobes with single stepping support
  2015-01-19  9:03       ` Pratyush Anand
@ 2015-01-21 18:02         ` David Long
  0 siblings, 0 replies; 21+ messages in thread
From: David Long @ 2015-01-21 18:02 UTC (permalink / raw)
  To: Pratyush Anand, Pratyush Anand
  Cc: Jon Medhurst (Tixy),
	Steve Capper, Ananth N Mavinakayanahalli, Sandeepa Prabhu,
	Catalin Marinas, Will Deacon, linux-kernel, Anil S Keshavamurthy,
	Masami Hiramatsu, Russell King, William Cohen, davem,
	linux-arm-kernel, oleg Nesterov

On 01/19/15 04:03, Pratyush Anand wrote:
>
>
> On Saturday 17 January 2015 12:58 AM, David Long wrote:
>>>> +static bool aarch64_insn_is_steppable(u32 insn)
>>>> +{
>>>> +       if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
>>>> +               if (aarch64_insn_is_branch(insn))
>>>> +                       return false;
>>>> +
>>>> +               /* modification of daif creates issues */
>>>> +               if (aarch64_insn_is_msr_daif(insn))
>>>> +                       return false;
>>>> +
>>>> +               if (aarch64_insn_is_hint(insn))
>>>> +                       return aarch64_insn_is_nop(insn);
>>>> +
>>>> +               return true;
>>>> +       }
>>>> +
>>>> +       if (aarch64_insn_uses_literal(insn))
>>>> +               return false;
>>>> +
>>>> +       if (aarch64_insn_is_exclusive(insn))
>>>> +               return false;
>>>> +
>>>> +       return true;
>>>
>>> Default true return may not be a good idea until we are sure that we
>>> are returning false for all possible
>>> simulation and rejection cases. In my opinion, its better to return
>>> true only for steppable and false for
>>> all remaining.
>>>
>>
>> I struggled a little with this when I did it but I decided if the
>> question was:  "should we have to recognize every instruction before
>> deciding it was single-steppable or should we only recognize
>> instructions that are *not* single-steppable", maybe it was OK to do the
>> latter while recognizing extensions to the instruction set *could* end
>> up (temporarly) allowing us to try and fail (badly) at single-stepping
>> any problematic new instructions.  Certainly opinions could differ.  If
>
> Lets see what others say, but I see that this approach will result in
> undesired behavior. For example: a probe has been tried to insert to svc
> instruction. SVC or any other exception generation instruction is
> expected to be rejected. But, current aarch64_insn_is_steppable will
> return true for it and then kprobe/uprobe code will allow to insert
> probe at that instruction, which will be wrong, no? I mean, I do not see
> a way to get into last else (INSN_REJECTED) of arm_kprobe_decode_insn.
>
> So, if we go with this approach we need to insure that we cover all
> simulation-able and reject-able cases in aarch64_insn_is_steppable.
>

yes, of course.  Any case that's missing in the current code needs to be 
fixed.  If the result starts to look less practical than the 
table-driven code then the new approach needs to be discarded.

> ~Pratyush
>
>
>
>> the consensus is that we can't allow this to ever happen (because old
>> kprobe code is running on new hardware) then I think the only choice is
>> to return to parsing binary tables.  Hopefully I could still find a way
>> to leverage insn.c in that case.


^ permalink raw reply	[flat|nested] 21+ messages in thread

end of thread, other threads:[~2015-01-21 18:03 UTC | newest]

Thread overview: 21+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-01-11  4:03 [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support David Long
2015-01-11  4:03 ` [PATCH v4 1/6] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature David Long
2015-01-12 12:51   ` Steve Capper
2015-01-15  7:07     ` Masami Hiramatsu
2015-01-11  4:03 ` [PATCH v4 2/6] arm64: Add more test functions to insn.c David Long
2015-01-14  9:32   ` Pratyush Anand
2015-01-16 21:27     ` David Long
2015-01-11  4:03 ` [PATCH v4 3/6] arm64: Kprobes with single stepping support David Long
2015-01-12 13:31   ` Steve Capper
2015-01-14  9:30   ` Pratyush Anand
2015-01-16 19:28     ` David Long
2015-01-19  9:03       ` Pratyush Anand
2015-01-21 18:02         ` David Long
2015-01-11  4:03 ` [PATCH v4 4/6] arm64: Kprobes instruction simulation support David Long
2015-01-14  9:32   ` Pratyush Anand
2015-01-16 21:34     ` David Long
2015-01-11  4:03 ` [PATCH v4 5/6] arm64: Add kernel return probes support(kretprobes) David Long
2015-01-12 14:01   ` Steve Capper
2015-01-11  4:03 ` [PATCH v4 6/6] kprobes: Add arm64 case in kprobe example module David Long
2015-01-12 14:09 ` [PATCH v4 0/6] arm64: Add kernel probes (kprobes) support Steve Capper
2015-01-14 11:55   ` Pratyush Anand

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