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Subject[PATCH 3/4] x86_64 ia32 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/ia32/ia32entry.S | 78 +++++++++++++++++++++++++++++++++++++++++---
arch/x86/kernel/entry_64.S | 1 +
2 files changed, 74 insertions(+), 5 deletions(-)

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index b5e329d..f38a354 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -15,6 +15,11 @@
#include <asm/irqflags.h>
#include <linux/linkage.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
+
#define IA32_NR_syscalls ((ia32_syscall_end - ia32_sys_call_table)/8)

.macro IA32_ARG_FIXUP noebp=0
@@ -131,13 +136,17 @@ sysenter_do_call:
cmpl $(IA32_NR_syscalls-1),%eax
ja ia32_badsys
IA32_ARG_FIXUP 1
+sysenter_dispatch:
call *ia32_sys_call_table(,%rax,8)
movq %rax,RAX-ARGOFFSET(%rsp)
GET_THREAD_INFO(%r10)
cli
TRACE_IRQS_OFF
- testl $_TIF_ALLWORK_MASK,threadinfo_flags(%r10)
+ testl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),threadinfo_flags(%r10)
jnz int_ret_from_sys_call
+ bt $TIF_SYSCALL_AUDIT,threadinfo_flags(%r10)
+ jc sysexit_audit
+sysexit_from_sys_call:
andl $~TS_COMPAT,threadinfo_status(%r10)
/* clear IF, that popfq doesn't enable interrupts early */
andl $~0x200,EFLAGS-R11(%rsp)
@@ -156,9 +165,56 @@ sysenter_do_call:
/* sysexit */
.byte 0xf, 0x35

-sysenter_tracesys:
+ .macro auditsys_entry dispatch
+ movl %esi,%r9d /* 6th arg: 4th syscall arg */
+ movl %edx,%r8d /* 5th arg: 3rd syscall arg */
+ /* (already in %ecx) 4th arg: 2nd syscall arg */
+ movl %ebx,%edx /* 3rd arg: 1st syscall arg */
+ movl %eax,%esi /* 2nd arg: syscall number */
+ movl $AUDIT_ARCH_I386,%edi /* 1st arg: audit arch */
+ call audit_syscall_entry
+ movl RAX-ARGOFFSET(%rsp),%eax /* reload syscall number */
+ cmpl $(IA32_NR_syscalls-1),%eax
+ ja ia32_badsys
+ movl %ebx,%edi /* reload 1st syscall arg */
+ movl RCX-ARGOFFSET(%rsp),%esi /* reload 2nd syscall arg */
+ movl RDX-ARGOFFSET(%rsp),%edx /* reload 3rd syscall arg */
+ movl RSI-ARGOFFSET(%rsp),%ecx /* reload 4th syscall arg */
+ movl RDI-ARGOFFSET(%rsp),%r8d /* reload 5th syscall arg */
+ movl %ebp,%r9d /* reload 6th syscall arg */
+ jmp \dispatch
+ .endm
+
+ .macro auditsys_exit exit
+ TRACE_IRQS_ON
+ sti
+ movl %eax,%esi /* second arg, syscall return value */
+ cmpl $0,%eax /* is it < 0? */
+ setl %al /* 1 if so, 0 if not */
+ movzbl %al,%edi /* zero-extend that into %edi */
+ inc %edi /* first arg, 0->1(AUDITSC_SUCCESS), 1->2(AUDITSC_FAILURE) */
+ call audit_syscall_exit
+ GET_THREAD_INFO(%r10)
+ movl RAX-ARGOFFSET(%rsp),%eax /* reload syscall return value */
+ movl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),%edi
+ cli
+ TRACE_IRQS_OFF
+ testl %edi,threadinfo_flags(%r10)
+ jnz int_with_check
+ jmp \exit
+ .endm
+
+sysenter_auditsys:
CFI_RESTORE_STATE
+ auditsys_entry sysenter_dispatch
+
+sysexit_audit:
+ auditsys_exit sysexit_from_sys_call
+
+sysenter_tracesys:
xchgl %r9d,%ebp
+ testl $(_TIF_SYSCALL_TRACE|_TIF_SECCOMP),threadinfo_flags(%r10)
+ jz sysenter_auditsys
SAVE_REST
CLEAR_RREGS
movq %r9,R9(%rsp)
@@ -238,13 +294,17 @@ cstar_do_call:
cmpl $IA32_NR_syscalls-1,%eax
ja ia32_badsys
IA32_ARG_FIXUP 1
+cstar_dispatch:
call *ia32_sys_call_table(,%rax,8)
movq %rax,RAX-ARGOFFSET(%rsp)
GET_THREAD_INFO(%r10)
cli
TRACE_IRQS_OFF
- testl $_TIF_ALLWORK_MASK,threadinfo_flags(%r10)
- jnz int_ret_from_sys_call
+ testl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),threadinfo_flags(%r10)
+ jnz int_ret_from_sys_call
+ bt $TIF_SYSCALL_AUDIT,threadinfo_flags(%r10)
+ jc sysretl_audit
+sysretl_from_sys_call:
andl $~TS_COMPAT,threadinfo_status(%r10)
RESTORE_ARGS 1,-ARG_SKIP,1,1,1
movl RIP-ARGOFFSET(%rsp),%ecx
@@ -257,9 +317,17 @@ cstar_do_call:
swapgs
sysretl

-cstar_tracesys:
+cstar_auditsys:
CFI_RESTORE_STATE
+ auditsys_entry cstar_dispatch
+
+sysretl_audit:
+ auditsys_exit sysretl_from_sys_call
+
+cstar_tracesys:
xchgl %r9d,%ebp
+ testl $(_TIF_SYSCALL_TRACE|_TIF_SECCOMP),threadinfo_flags(%r10)
+ jz cstar_auditsys
SAVE_REST
CLEAR_RREGS
movq %r9,R9(%rsp)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 9b152d5..01c3e6b 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -375,6 +375,7 @@ tracesys:
* Has correct top of stack, but partial stack frame.
*/
.globl int_ret_from_sys_call
+ .globl int_with_check
int_ret_from_sys_call:
DISABLE_INTERRUPTS(CLBR_NONE)
TRACE_IRQS_OFF

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