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From: Denys Vlasenko <dvlasenk@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Oleg Nesterov <oleg@redhat.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Alexei Starovoitov <ast@plumgrid.com>,
	Will Drewry <wad@chromium.org>, Kees Cook <keescook@chromium.org>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2] x86/asm/entry/32: Update ENOSYS handling to match 64-bit logic
Date: Tue, 21 Apr 2015 18:03:14 +0200	[thread overview]
Message-ID: <1429632194-13445-2-git-send-email-dvlasenk@redhat.com> (raw)
In-Reply-To: <1429632194-13445-1-git-send-email-dvlasenk@redhat.com>

Sometime ago Andy changed 64-bit syscall logic so that pt_regs->ax is
initially set to -ENOSYS, and on exit from syscall, it is updated with
actual return value. This simplified logic there.

This patch does the same for 32-bit syscall entry points.

The check for %rax being too big is moved to be just before
the call insn which dispatches execution through syscall table.
There is no way to accidentally skip this check now by jumping
to a label after it. This allows to remove redundant checks
after e.g. ptrace.

If %rax is too big, we just skip over the (call, write %rax to pt_regs->ax)
insn pair. pt_regs->ax remains set to -ENOSYS, and it gets returned
to userspace.

Similar to 64-bit code, this eliminates "ia32_badsys" code path.

Run-tested.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@kernel.org>
CC: Borislav Petkov <bp@alien8.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Alexei Starovoitov <ast@plumgrid.com>
CC: Will Drewry <wad@chromium.org>
CC: Kees Cook <keescook@chromium.org>
CC: x86@kernel.org
CC: linux-kernel@vger.kernel.org
---

Changes in v2: fixed an error: changing RAX to ORIG_RAX in
    movq ORIG_RAX(%rsp),%rax        /* reload syscall return value */
was wrong.

 arch/x86/ia32/ia32entry.S | 44 +++++++++++++++-----------------------------
 1 file changed, 15 insertions(+), 29 deletions(-)

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index a821b1c..29ab1c2 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -142,7 +142,7 @@ ENTRY(ia32_sysenter_target)
 	pushq_cfi_reg	rsi			/* pt_regs->si */
 	pushq_cfi_reg	rdx			/* pt_regs->dx */
 	pushq_cfi_reg	rcx			/* pt_regs->cx */
-	pushq_cfi_reg	rax			/* pt_regs->ax */
+	pushq_cfi	$-ENOSYS		/* pt_regs->ax */
 	cld
 	sub	$(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
 	CFI_ADJUST_CFA_OFFSET 10*8
@@ -169,8 +169,6 @@ sysenter_flags_fixed:
 	testl   $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	CFI_REMEMBER_STATE
 	jnz  sysenter_tracesys
-	cmpq	$(IA32_NR_syscalls-1),%rax
-	ja	ia32_badsys
 sysenter_do_call:
 	/* 32bit syscall -> 64bit C ABI argument conversion */
 	movl	%edi,%r8d	/* arg5 */
@@ -179,8 +177,11 @@ sysenter_do_call:
 	movl	%ebx,%edi	/* arg1 */
 	movl	%edx,%edx	/* arg3 (zero extension) */
 sysenter_dispatch:
+	cmpq	$(IA32_NR_syscalls-1),%rax
+	ja	1f
 	call	*ia32_sys_call_table(,%rax,8)
 	movq	%rax,RAX(%rsp)
+1:
 	DISABLE_INTERRUPTS(CLBR_NONE)
 	TRACE_IRQS_OFF
 	testl	$_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
@@ -247,9 +248,7 @@ sysexit_from_sys_call:
 	movl %ebx,%esi			/* 2nd arg: 1st syscall arg */
 	movl %eax,%edi			/* 1st arg: syscall number */
 	call __audit_syscall_entry
-	movl RAX(%rsp),%eax	/* reload syscall number */
-	cmpq $(IA32_NR_syscalls-1),%rax
-	ja ia32_badsys
+	movl ORIG_RAX(%rsp),%eax	/* reload syscall number */
 	movl %ebx,%edi			/* reload 1st syscall arg */
 	movl RCX(%rsp),%esi	/* reload 2nd syscall arg */
 	movl RDX(%rsp),%edx	/* reload 3rd syscall arg */
@@ -300,13 +299,10 @@ sysenter_tracesys:
 #endif
 	SAVE_EXTRA_REGS
 	CLEAR_RREGS
-	movq	$-ENOSYS,RAX(%rsp)/* ptrace can change this for a bad syscall */
 	movq	%rsp,%rdi        /* &pt_regs -> arg1 */
 	call	syscall_trace_enter
 	LOAD_ARGS32  /* reload args from stack in case ptrace changed it */
 	RESTORE_EXTRA_REGS
-	cmpq	$(IA32_NR_syscalls-1),%rax
-	ja	int_ret_from_sys_call /* sysenter_tracesys has set RAX(%rsp) */
 	jmp	sysenter_do_call
 	CFI_ENDPROC
 ENDPROC(ia32_sysenter_target)
@@ -376,7 +372,7 @@ ENTRY(ia32_cstar_target)
 	pushq_cfi_reg	rdx			/* pt_regs->dx */
 	pushq_cfi_reg	rbp			/* pt_regs->cx */
 	movl	%ebp,%ecx
-	pushq_cfi_reg	rax			/* pt_regs->ax */
+	pushq_cfi	$-ENOSYS		/* pt_regs->ax */
 	sub	$(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
 	CFI_ADJUST_CFA_OFFSET 10*8
 
@@ -392,8 +388,6 @@ ENTRY(ia32_cstar_target)
 	testl   $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	CFI_REMEMBER_STATE
 	jnz   cstar_tracesys
-	cmpq $IA32_NR_syscalls-1,%rax
-	ja  ia32_badsys
 cstar_do_call:
 	/* 32bit syscall -> 64bit C ABI argument conversion */
 	movl	%edi,%r8d	/* arg5 */
@@ -402,8 +396,11 @@ cstar_do_call:
 	movl	%ebx,%edi	/* arg1 */
 	movl	%edx,%edx	/* arg3 (zero extension) */
 cstar_dispatch:
+	cmpq	$(IA32_NR_syscalls-1),%rax
+	ja	1f
 	call *ia32_sys_call_table(,%rax,8)
 	movq %rax,RAX(%rsp)
+1:
 	DISABLE_INTERRUPTS(CLBR_NONE)
 	TRACE_IRQS_OFF
 	testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
@@ -450,14 +447,11 @@ cstar_tracesys:
 	xchgl %r9d,%ebp
 	SAVE_EXTRA_REGS
 	CLEAR_RREGS r9
-	movq $-ENOSYS,RAX(%rsp)	/* ptrace can change this for a bad syscall */
 	movq %rsp,%rdi        /* &pt_regs -> arg1 */
 	call syscall_trace_enter
 	LOAD_ARGS32 1	/* reload args from stack in case ptrace changed it */
 	RESTORE_EXTRA_REGS
 	xchgl %ebp,%r9d
-	cmpq $(IA32_NR_syscalls-1),%rax
-	ja int_ret_from_sys_call /* cstar_tracesys has set RAX(%rsp) */
 	jmp cstar_do_call
 END(ia32_cstar_target)
 				
@@ -516,7 +510,7 @@ ENTRY(ia32_syscall)
 	pushq_cfi_reg	rsi			/* pt_regs->si */
 	pushq_cfi_reg	rdx			/* pt_regs->dx */
 	pushq_cfi_reg	rcx			/* pt_regs->cx */
-	pushq_cfi_reg	rax			/* pt_regs->ax */
+	pushq_cfi	$-ENOSYS		/* pt_regs->ax */
 	cld
 	sub	$(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
 	CFI_ADJUST_CFA_OFFSET 10*8
@@ -524,8 +518,6 @@ ENTRY(ia32_syscall)
 	orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
 	testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	jnz ia32_tracesys
-	cmpq $(IA32_NR_syscalls-1),%rax
-	ja ia32_badsys
 ia32_do_call:
 	/* 32bit syscall -> 64bit C ABI argument conversion */
 	movl %edi,%r8d	/* arg5 */
@@ -533,9 +525,12 @@ ia32_do_call:
 	xchg %ecx,%esi	/* rsi:arg2, rcx:arg4 */
 	movl %ebx,%edi	/* arg1 */
 	movl %edx,%edx	/* arg3 (zero extension) */
+	cmpq	$(IA32_NR_syscalls-1),%rax
+	ja	1f
 	call *ia32_sys_call_table(,%rax,8) # xxx: rip relative
 ia32_sysret:
 	movq %rax,RAX(%rsp)
+1:
 ia32_ret_from_sys_call:
 	CLEAR_RREGS
 	jmp int_ret_from_sys_call
@@ -543,23 +538,14 @@ ia32_ret_from_sys_call:
 ia32_tracesys:
 	SAVE_EXTRA_REGS
 	CLEAR_RREGS
-	movq $-ENOSYS,RAX(%rsp)	/* ptrace can change this for a bad syscall */
 	movq %rsp,%rdi        /* &pt_regs -> arg1 */
 	call syscall_trace_enter
 	LOAD_ARGS32	/* reload args from stack in case ptrace changed it */
 	RESTORE_EXTRA_REGS
-	cmpq $(IA32_NR_syscalls-1),%rax
-	ja  int_ret_from_sys_call	/* ia32_tracesys has set RAX(%rsp) */
 	jmp ia32_do_call
+	CFI_ENDPROC
 END(ia32_syscall)
 
-ia32_badsys:
-	movq $0,ORIG_RAX(%rsp)
-	movq $-ENOSYS,%rax
-	jmp ia32_sysret
-
-	CFI_ENDPROC
-	
 	.macro PTREGSCALL label, func
 	ALIGN
 GLOBAL(\label)
-- 
1.8.1.4


  reply	other threads:[~2015-04-21 16:03 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-04-21 16:03 [PATCH v2] x86/asm/entry/64: 32-bit execve stubs are identical to x32 ones, merge them Denys Vlasenko
2015-04-21 16:03 ` Denys Vlasenko [this message]
2015-04-22 14:11   ` [tip:x86/asm] x86/asm/entry/32: Update -ENOSYS handling to match the 64-bit logic tip-bot for Denys Vlasenko
2015-04-22 14:07 ` [PATCH v2] x86/asm/entry/64: 32-bit execve stubs are identical to x32 ones, merge them Brian Gerst
2015-04-22 14:11 ` [tip:x86/asm] x86/asm/entry/64: Merge 32-bit execve stubs with x32 ones, as they are identical tip-bot for Denys Vlasenko
  -- strict thread matches above, loose matches on Subject: below --
2015-04-10 15:33 [PATCH] x86/asm/entry/32: Update ENOSYS handling to match 64-bit logic Denys Vlasenko
2015-04-10 16:22 ` [PATCH v2] " Denys Vlasenko

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