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Subject[PATCH 4/4] i386 syscall audit fast-path
Date
This adds fast paths for 32-bit syscall entry and exit when
TIF_SYSCALL_AUDIT is set, but no other kind of syscall tracing.
These paths does not need to save and restore all registers as
the general case of tracing does. Avoiding the iret return path
when syscall audit is enabled helps performance a lot.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
arch/x86/kernel/entry_32.S | 48 ++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index c778e4f..daf1361 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -53,6 +53,11 @@
#include <asm/processor-flags.h>
#include "irq_vectors.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
+
/*
* We use macros for low-level operations which need to be overridden
* for paravirtualization. The following will never clobber any registers:
@@ -332,7 +337,8 @@ sysenter_past_esp:

/* Note, _TIF_SECCOMP is bit number 8, and so it needs testw and not testb */
testw $(_TIF_SYSCALL_EMU|_TIF_SYSCALL_TRACE|_TIF_SECCOMP|_TIF_SYSCALL_AUDIT),TI_flags(%ebp)
- jnz syscall_trace_entry
+ jnz sysenter_audit
+sysenter_do_call:
cmpl $(nr_syscalls), %eax
jae syscall_badsys
call *sys_call_table(,%eax,4)
@@ -342,7 +348,8 @@ sysenter_past_esp:
TRACE_IRQS_OFF
movl TI_flags(%ebp), %ecx
testw $_TIF_ALLWORK_MASK, %cx
- jne syscall_exit_work
+ jne sysexit_audit
+sysenter_exit:
/* if something modifies registers it must also disable sysexit */
movl PT_EIP(%esp), %edx
movl PT_OLDESP(%esp), %ecx
@@ -350,6 +357,43 @@ sysenter_past_esp:
TRACE_IRQS_ON
1: mov PT_FS(%esp), %fs
ENABLE_INTERRUPTS_SYSCALL_RET
+
+sysenter_audit:
+ testw $(_TIF_SYSCALL_EMU|_TIF_SYSCALL_TRACE|_TIF_SECCOMP),TI_flags(%ebp)
+ jnz syscall_trace_entry
+ addl $4,%esp
+ CFI_ADJUST_CFA_OFFSET -4
+ /* %esi already in 8(%esp) 6th arg: 4th syscall arg */
+ /* %edx already in 4(%esp) 5th arg: 3rd syscall arg */
+ /* %ecx already in 0(%esp) 4th arg: 2nd syscall arg */
+ movl %ebx,%ecx /* 3rd arg: 1st syscall arg */
+ movl %eax,%edx /* 2nd arg: syscall number */
+ movl $AUDIT_ARCH_I386,%eax /* 1st arg: audit arch */
+ call audit_syscall_entry
+ pushl %ebx
+ CFI_ADJUST_CFA_OFFSET 4
+ movl PT_EAX(%esp),%eax /* reload syscall number */
+ jmp sysenter_do_call
+
+sysexit_audit:
+ testw $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT), %cx
+ jne syscall_exit_work
+ TRACE_IRQS_ON
+ ENABLE_INTERRUPTS(CLBR_ANY)
+ movl %eax,%edx /* second arg, syscall return value */
+ cmpl $0,%eax /* is it < 0? */
+ setl %al /* 1 if so, 0 if not */
+ movzbl %al,%eax /* zero-extend that */
+ inc %eax /* first arg, 0->1(AUDITSC_SUCCESS), 1->2(AUDITSC_FAILURE) */
+ call audit_syscall_exit
+ DISABLE_INTERRUPTS(CLBR_ANY)
+ TRACE_IRQS_OFF
+ movl TI_flags(%ebp), %ecx
+ testw $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT), %cx
+ jne syscall_exit_work
+ movl PT_EAX(%esp),%eax /* reload syscall return value */
+ jmp sysenter_exit
+
CFI_ENDPROC
.pushsection .fixup,"ax"
2: movl $0,PT_FS(%esp)

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