x86, smap: Add STAC and CLAC instructions to control user space access
When Supervisor Mode Access Prevention (SMAP) is enabled, access to
userspace from the kernel is controlled by the AC flag. To make the
performance of manipulating that flag acceptable, there are two new
instructions, STAC and CLAC, to set and clear it.
This patch adds those instructions, via alternative(), when the SMAP
feature is enabled. It also adds X86_EFLAGS_AC unconditionally to the
SYSCALL entry mask; there is simply no reason to make that one
conditional.
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1348256595-29119-9-git-send-email-hpa@linux.intel.com
diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index 5b2995f..a30ca15 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -17,6 +17,7 @@
#include <asm/cpufeature.h>
#include <asm/alternative-asm.h>
#include <asm/asm.h>
+#include <asm/smap.h>
/*
* By placing feature2 after feature1 in altinstructions section, we logically
@@ -130,6 +131,7 @@
*/
ENTRY(copy_user_generic_unrolled)
CFI_STARTPROC
+ ASM_STAC
cmpl $8,%edx
jb 20f /* less then 8 bytes, go to byte copy loop */
ALIGN_DESTINATION
@@ -177,6 +179,7 @@
decl %ecx
jnz 21b
23: xor %eax,%eax
+ ASM_CLAC
ret
.section .fixup,"ax"
@@ -232,6 +235,7 @@
*/
ENTRY(copy_user_generic_string)
CFI_STARTPROC
+ ASM_STAC
andl %edx,%edx
jz 4f
cmpl $8,%edx
@@ -246,6 +250,7 @@
3: rep
movsb
4: xorl %eax,%eax
+ ASM_CLAC
ret
.section .fixup,"ax"
@@ -273,12 +278,14 @@
*/
ENTRY(copy_user_enhanced_fast_string)
CFI_STARTPROC
+ ASM_STAC
andl %edx,%edx
jz 2f
movl %edx,%ecx
1: rep
movsb
2: xorl %eax,%eax
+ ASM_CLAC
ret
.section .fixup,"ax"