Commit c5f69fde authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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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: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eric Paris <eparis@parisplace.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/212be39dd8c90b44c4b7bbc678128d6b88bdb9912.1438378274.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent decd275e

arch/x86/entry/entry_32.S

+2 −46
Original line number Diff line number Diff line
@@ -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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