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/getuser.S b/arch/x86/lib/getuser.S
index b33b1fb..156b9c8 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -33,6 +33,7 @@
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>
#include <asm/asm.h>
+#include <asm/smap.h>
.text
ENTRY(__get_user_1)
@@ -40,8 +41,10 @@
GET_THREAD_INFO(%_ASM_DX)
cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
+ ASM_STAC
1: movzb (%_ASM_AX),%edx
xor %eax,%eax
+ ASM_CLAC
ret
CFI_ENDPROC
ENDPROC(__get_user_1)
@@ -53,8 +56,10 @@
GET_THREAD_INFO(%_ASM_DX)
cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
+ ASM_STAC
2: movzwl -1(%_ASM_AX),%edx
xor %eax,%eax
+ ASM_CLAC
ret
CFI_ENDPROC
ENDPROC(__get_user_2)
@@ -66,8 +71,10 @@
GET_THREAD_INFO(%_ASM_DX)
cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
+ ASM_STAC
3: mov -3(%_ASM_AX),%edx
xor %eax,%eax
+ ASM_CLAC
ret
CFI_ENDPROC
ENDPROC(__get_user_4)
@@ -80,8 +87,10 @@
GET_THREAD_INFO(%_ASM_DX)
cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
+ ASM_STAC
4: movq -7(%_ASM_AX),%_ASM_DX
xor %eax,%eax
+ ASM_CLAC
ret
CFI_ENDPROC
ENDPROC(__get_user_8)
@@ -91,6 +100,7 @@
CFI_STARTPROC
xor %edx,%edx
mov $(-EFAULT),%_ASM_AX
+ ASM_CLAC
ret
CFI_ENDPROC
END(bad_get_user)