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From: Andrey Konovalov <andreyknvl@google.com>
To: "Andrey Ryabinin" <aryabinin@virtuozzo.com>,
	"Alexander Potapenko" <glider@google.com>,
	"Dmitry Vyukov" <dvyukov@google.com>,
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	kasan-dev@googlegroups.com, linux-doc@vger.kernel.org,
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Cc: Kostya Serebryany <kcc@google.com>,
	Evgeniy Stepanov <eugenis@google.com>,
	Lee Smith <Lee.Smith@arm.com>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
	Jacob Bramley <Jacob.Bramley@arm.com>,
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	Kees Cook <keescook@google.com>, Jann Horn <jannh@google.com>,
	Mark Brand <markbrand@google.com>,
	Chintan Pandya <cpandya@codeaurora.org>
Subject: [PATCH v1 14/16] khwasan, arm64: add brk handler for inline instrumentation
Date: Tue,  8 May 2018 19:21:00 +0200	[thread overview]
Message-ID: <1259ed7ecd6e47925184964db90139bc9ef29426.1525798754.git.andreyknvl@google.com> (raw)
In-Reply-To: <cover.1525798753.git.andreyknvl@google.com>
In-Reply-To: <cover.1525798753.git.andreyknvl@google.com>

KHWASAN inline instrumentation mode (which embeds checks of shadow memory
into the generated code, instead of inserting a callback) generates a brk
instruction when a tag mismatch is detected.

This commit add a KHWASAN brk handler, that decodes the immediate value
passed to the brk instructions (to extract information about the memory
access that triggered the mismatch), reads the register values (x0 contains
the guilty address) and reports the bug.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/include/asm/brk-imm.h |  2 +
 arch/arm64/kernel/traps.c        | 69 +++++++++++++++++++++++++++++++-
 2 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h
index ed693c5bcec0..e4a7013321dc 100644
--- a/arch/arm64/include/asm/brk-imm.h
+++ b/arch/arm64/include/asm/brk-imm.h
@@ -16,10 +16,12 @@
  * 0x400: for dynamic BRK instruction
  * 0x401: for compile time BRK instruction
  * 0x800: kernel-mode BUG() and WARN() traps
+ * 0x9xx: KHWASAN trap (allowed values 0x900 - 0x9ff)
  */
 #define FAULT_BRK_IMM			0x100
 #define KGDB_DYN_DBG_BRK_IMM		0x400
 #define KGDB_COMPILED_DBG_BRK_IMM	0x401
 #define BUG_BRK_IMM			0x800
+#define KHWASAN_BRK_IMM			0x900
 
 #endif
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 8bbdc17e49df..2234e3a4cc35 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -35,6 +35,7 @@
 #include <linux/sizes.h>
 #include <linux/syscalls.h>
 #include <linux/mm_types.h>
+#include <linux/kasan.h>
 
 #include <asm/atomic.h>
 #include <asm/bug.h>
@@ -269,10 +270,14 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
 	}
 }
 
-void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
+void __arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
 {
 	regs->pc += size;
+}
 
+void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
+{
+	__arm64_skip_faulting_instruction(regs, size);
 	/*
 	 * If we were single stepping, we want to get the step exception after
 	 * we return from the trap.
@@ -790,7 +795,7 @@ static int bug_handler(struct pt_regs *regs, unsigned int esr)
 	}
 
 	/* If thread survives, skip over the BUG instruction and continue: */
-	arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
+	__arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
 	return DBG_HOOK_HANDLED;
 }
 
@@ -800,6 +805,59 @@ static struct break_hook bug_break_hook = {
 	.fn = bug_handler,
 };
 
+#ifdef CONFIG_KASAN_HW
+
+#define KHWASAN_ESR_RECOVER	0x20
+#define KHWASAN_ESR_WRITE	0x10
+#define KHWASAN_ESR_SIZE_MASK	0x0f
+#define KHWASAN_ESR_SIZE(esr)	(1 << ((esr) & KHWASAN_ESR_SIZE_MASK))
+
+static int khwasan_handler(struct pt_regs *regs, unsigned int esr)
+{
+	bool recover = esr & KHWASAN_ESR_RECOVER;
+	bool write = esr & KHWASAN_ESR_WRITE;
+	size_t size = KHWASAN_ESR_SIZE(esr);
+	u64 addr = regs->regs[0];
+	u64 pc = regs->pc;
+
+	if (user_mode(regs))
+		return DBG_HOOK_ERROR;
+
+	kasan_report(addr, size, write, pc);
+
+	/*
+	 * The instrumentation allows to control whether we can proceed after
+	 * a crash was detected. This is done by passing the -recover flag to
+	 * the compiler. Disabling recovery allows to generate more compact
+	 * code.
+	 *
+	 * Unfortunately disabling recovery doesn't work for the kernel right
+	 * now. KHWASAN reporting is disabled in some contexts (for example when
+	 * the allocator accesses slab object metadata; same is true for KASAN;
+	 * this is controlled by current->kasan_depth). All these accesses are
+	 * detected by the tool, even though the reports for them are not
+	 * printed.
+	 *
+	 * This is something that might be fixed at some point in the future.
+	 */
+	if (!recover)
+		die("Oops - KHWASAN", regs, 0);
+
+	/* If thread survives, skip over the brk instruction and continue: */
+	__arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
+	return DBG_HOOK_HANDLED;
+}
+
+#define KHWASAN_ESR_VAL (0xf2000000 | KHWASAN_BRK_IMM)
+#define KHWASAN_ESR_MASK 0xffffff00
+
+static struct break_hook khwasan_break_hook = {
+	.esr_val = KHWASAN_ESR_VAL,
+	.esr_mask = KHWASAN_ESR_MASK,
+	.fn = khwasan_handler,
+};
+#endif
+
 /*
  * Initial handler for AArch64 BRK exceptions
  * This handler only used until debug_traps_init().
@@ -807,6 +865,10 @@ static struct break_hook bug_break_hook = {
 int __init early_brk64(unsigned long addr, unsigned int esr,
 		struct pt_regs *regs)
 {
+#ifdef CONFIG_KASAN_HW
+	if ((esr & KHWASAN_ESR_MASK) == KHWASAN_ESR_VAL)
+		return khwasan_handler(regs, esr) != DBG_HOOK_HANDLED;
+#endif
 	return bug_handler(regs, esr) != DBG_HOOK_HANDLED;
 }
 
@@ -814,4 +876,7 @@ int __init early_brk64(unsigned long addr, unsigned int esr,
 void __init trap_init(void)
 {
 	register_break_hook(&bug_break_hook);
+#ifdef CONFIG_KASAN_HW
+	register_break_hook(&khwasan_break_hook);
+#endif
 }
-- 
2.17.0.441.gb46fe60e1d-goog

  parent reply	other threads:[~2018-05-08 17:21 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-08 17:20 [PATCH v1 00/16] khwasan: kernel hardware assisted address sanitizer Andrey Konovalov
2018-05-08 17:20 ` [PATCH v1 01/16] khwasan, mm: change kasan hooks signatures Andrey Konovalov
2018-05-14 16:56   ` Andrey Ryabinin
2018-05-08 17:20 ` [PATCH v1 02/16] khwasan: move common kasan and khwasan code to common.c Andrey Konovalov
2018-05-15 13:28   ` Andrey Ryabinin
2018-05-08 17:20 ` [PATCH v1 03/16] khwasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW Andrey Konovalov
2018-05-14 16:57   ` Andrey Ryabinin
2018-05-08 17:20 ` [PATCH v1 04/16] khwasan, arm64: adjust shadow size for CONFIG_KASAN_HW Andrey Konovalov
2018-05-08 17:20 ` [PATCH v1 05/16] khwasan: initialize shadow to 0xff Andrey Konovalov
2018-05-08 17:20 ` [PATCH v1 06/16] khwasan, arm64: untag virt address in __kimg_to_phys Andrey Konovalov
2018-05-08 17:20 ` [PATCH v1 07/16] khwasan, arm64: fix up fault handling logic Andrey Konovalov
2018-05-08 17:20 ` [PATCH v1 08/16] khwasan: add tag related helper functions Andrey Konovalov
2018-05-14 16:58   ` Andrey Ryabinin
2018-05-08 17:20 ` [PATCH v1 09/16] khwasan, arm64: enable top byte ignore for the kernel Andrey Konovalov
2018-05-08 17:20 ` [PATCH v1 10/16] khwasan, mm: perform untagged pointers comparison in krealloc Andrey Konovalov
2018-05-08 17:20 ` [PATCH v1 11/16] khwasan: split out kasan_report.c from report.c Andrey Konovalov
2018-05-08 17:20 ` [PATCH v1 12/16] khwasan: add bug reporting routines Andrey Konovalov
2018-05-08 17:20 ` [PATCH v1 13/16] khwasan: add hooks implementation Andrey Konovalov
2018-05-15 13:13   ` Andrey Ryabinin
2018-05-08 17:21 ` Andrey Konovalov [this message]
2018-05-08 17:21 ` [PATCH v1 15/16] khwasan, mm, arm64: tag non slab memory allocated via pagealloc Andrey Konovalov
2018-05-15 14:06   ` Andrey Ryabinin
2018-05-08 17:21 ` [PATCH v1 16/16] khwasan: update kasan documentation Andrey Konovalov
2018-05-09  5:26   ` Mike Rapoport
2018-05-09 12:13     ` Andrey Konovalov

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