[tip:x86/asm] x86/entry/32: Remove 32-bit syscall audit optimizations

[tip-bot for Andy Lutomirski]

Commit-ID:  c5f69fde26d1581ee495f68bb9de4049c8168a04
Gitweb:     http://git.kernel.org/tip/c5f69fde26d1581ee495f68bb9de4049c8168a04
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Fri, 31 Jul 2015 14:41:08 -0700
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 5 Aug 2015 10:54:35 +0200

x86/entry/32: Remove 32-bit syscall audit optimizations

The asm audit optimizations are ugly and obfuscate the code too
much. Remove them.

This will regress performance if syscall auditing is enabled on
32-bit kernels and SYSENTER is in use. If this becomes a
problem, interested parties are encouraged to implement the
equivalent of the 64-bit opportunistic SYSRET optimization.

Alternatively, a case could be made that, on 32-bit kernels, a
less messy asm audit optimization could be done. 32-bit kernels
don't have the complicated partial register saving tricks that
64-bit kernels have, so the SYSENTER post-syscall path could
just call the audit hooks directly.  Any reimplementation of
this ought to demonstrate that it only calls the audit hook once
per syscall, though, which does not currently appear to be true.

Someone would have to make the case that doing so would be
better than implementing opportunistic SYSEXIT, though.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: Eric Paris <eparis@xxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/212be39dd8c90b44c4b7bbc678128d6b88bdb9912.1438378274.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/entry/entry_32.S | 48 ++---------------------------------------------
 1 file changed, 2 insertions(+), 46 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index f940e24..a3c307a 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -45,16 +45,6 @@
 #include <asm/asm.h>
 #include <asm/smap.h>
 
-/* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this.  */
-#include <linux/elf-em.h>
-#define AUDIT_ARCH_I386		(EM_386|__AUDIT_ARCH_LE)
-#define __AUDIT_ARCH_LE		0x40000000
-
-#ifndef CONFIG_AUDITSYSCALL
-# define sysenter_audit		syscall_trace_entry
-# define sysexit_audit		syscall_exit_work
-#endif
-
 	.section .entry.text, "ax"
 
 /*
@@ -339,7 +329,7 @@ sysenter_past_esp:
 	GET_THREAD_INFO(%ebp)
 
 	testl	$_TIF_WORK_SYSCALL_ENTRY, TI_flags(%ebp)
-	jnz	sysenter_audit
+	jnz	syscall_trace_entry
 sysenter_do_call:
 	cmpl	$(NR_syscalls), %eax
 	jae	sysenter_badsys
@@ -351,7 +341,7 @@ sysenter_after_call:
 	TRACE_IRQS_OFF
 	movl	TI_flags(%ebp), %ecx
 	testl	$_TIF_ALLWORK_MASK, %ecx
-	jnz	sysexit_audit
+	jnz	syscall_exit_work
 sysenter_exit:
 /* if something modifies registers it must also disable sysexit */
 	movl	PT_EIP(%esp), %edx
@@ -362,40 +352,6 @@ sysenter_exit:
 	PTGS_TO_GS
 	ENABLE_INTERRUPTS_SYSEXIT
 
-#ifdef CONFIG_AUDITSYSCALL
-sysenter_audit:
-	testl	$(_TIF_WORK_SYSCALL_ENTRY & ~_TIF_SYSCALL_AUDIT), TI_flags(%ebp)
-	jnz	syscall_trace_entry
-	/* movl	PT_EAX(%esp), %eax already set, syscall number: 1st arg to audit */
-	movl	PT_EBX(%esp), %edx		/* ebx/a0: 2nd arg to audit */
-	/* movl	PT_ECX(%esp), %ecx already set, a1: 3nd arg to audit */
-	pushl	PT_ESI(%esp)			/* a3: 5th arg */
-	pushl	PT_EDX+4(%esp)			/* a2: 4th arg */
-	call	__audit_syscall_entry
-	popl	%ecx				/* get that remapped edx off the stack */
-	popl	%ecx				/* get that remapped esi off the stack */
-	movl	PT_EAX(%esp), %eax		/* reload syscall number */
-	jmp	sysenter_do_call
-
-sysexit_audit:
-	testl	$(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT), %ecx
-	jnz	syscall_exit_work
-	TRACE_IRQS_ON
-	ENABLE_INTERRUPTS(CLBR_ANY)
-	movl	%eax, %edx			/* second arg, syscall return value */
-	cmpl	$-MAX_ERRNO, %eax		/* is it an error ? */
-	setbe %al				/* 1 if so, 0 if not */
-	movzbl %al, %eax			/* zero-extend that */
-	call	__audit_syscall_exit
-	DISABLE_INTERRUPTS(CLBR_ANY)
-	TRACE_IRQS_OFF
-	movl	TI_flags(%ebp), %ecx
-	testl	$(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT), %ecx
-	jnz	syscall_exit_work
-	movl	PT_EAX(%esp), %eax		/* reload syscall return value */
-	jmp	sysenter_exit
-#endif
-
 .pushsection .fixup, "ax"
 2:	movl	$0, PT_FS(%esp)
 	jmp	1b
--
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