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Subject[PATCH 3/4] powerpc: Optimise 64bit syscall auditing entry path

Add an assembly fast path for the syscall audit entry path on
64bit. Some distros enable auditing by default which forces us
through the syscall auditing path even if there are no rules.

I wrote some test cases to validate the patch:

http://ozlabs.org/~anton/junkcode/audit_tests.tar.gz

And to test the performance I ran a simple null syscall
microbenchmark on a POWER7 box:

http://ozlabs.org/~anton/junkcode/null_syscall.c

Baseline: 949.2 cycles
Patched: 920.6 cycles

An improvement of 3%. Most of the potential gains are masked by
the syscall audit exit path which will be fixed in a
subsequent patch.

Signed-off-by: Anton Blanchard <anton@samba.org>
---

Index: b/arch/powerpc/kernel/entry_64.S
===================================================================
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -34,6 +34,12 @@
#include <asm/ftrace.h>
#include <asm/hw_irq.h>

+/* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this. */
+#include <linux/elf-em.h>
+#define AUDIT_ARCH_PPC (EM_PPC)
+#define AUDIT_ARCH_PPC64 (EM_PPC64|__AUDIT_ARCH_64BIT)
+#define __AUDIT_ARCH_64BIT 0x80000000
+
/*
* System calls.
*/
@@ -244,6 +250,10 @@ syscall_error:

/* Traced system call support */
syscall_dotrace:
+#ifdef CONFIG_AUDITSYSCALL
+ andi. r11,r10,(_TIF_SYSCALL_T_OR_A & ~_TIF_SYSCALL_AUDIT)
+ beq audit_entry
+#endif
bl .save_nvgprs
addi r3,r1,STACK_FRAME_OVERHEAD
bl .do_syscall_trace_enter
@@ -253,6 +263,7 @@ syscall_dotrace:
* for the call number to look up in the table (r0).
*/
mr r0,r3
+.Laudit_entry_return:
ld r3,GPR3(r1)
ld r4,GPR4(r1)
ld r5,GPR5(r1)
@@ -264,6 +275,34 @@ syscall_dotrace:
ld r10,TI_FLAGS(r10)
b .Lsyscall_dotrace_cont

+#ifdef CONFIG_AUDITSYSCALL
+audit_entry:
+ ld r4,GPR0(r1)
+ ld r5,GPR3(r1)
+ ld r6,GPR4(r1)
+ ld r7,GPR5(r1)
+ ld r8,GPR6(r1)
+
+ andi. r11,r10,_TIF_32BIT
+ beq 1f
+
+ lis r3,AUDIT_ARCH_PPC@h
+ ori r3,r3,AUDIT_ARCH_PPC@l
+ clrldi r5,r5,32
+ clrldi r6,r6,32
+ clrldi r7,r7,32
+ clrldi r8,r8,32
+ bl .__audit_syscall_entry
+ ld r0,GPR0(r1)
+ b .Laudit_entry_return
+
+1: lis r3,AUDIT_ARCH_PPC64@h
+ ori r3,r3,AUDIT_ARCH_PPC64@l
+ bl .__audit_syscall_entry
+ ld r0,GPR0(r1)
+ b .Laudit_entry_return
+#endif
+
syscall_enosys:
li r3,-ENOSYS
b syscall_exit

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