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

1 files changed, 7 insertions, 1 deletions

diff --git a/arch/x86/lib/putuser.S b/arch/x86/lib/putuser.S
index 7f951c8f76c4..fc6ba17a7eec 100644
--- a/arch/x86/lib/putuser.S
+++ b/arch/x86/lib/putuser.S
@@ -15,6 +15,7 @@
 #include <asm/thread_info.h>
 #include <asm/errno.h>
 #include <asm/asm.h>
+#include <asm/smap.h>
 
 
 /*
@@ -31,7 +32,8 @@
 
 #define ENTER   CFI_STARTPROC ; \
                 GET_THREAD_INFO(%_ASM_BX)
-#define EXIT    ret ; \
+#define EXIT    ASM_CLAC ;      \
+                ret ;           \
                 CFI_ENDPROC
 
 .text
@@ -39,6 +41,7 @@ ENTRY(__put_user_1)
         ENTER
         cmp TI_addr_limit(%_ASM_BX),%_ASM_CX
         jae bad_put_user
+        ASM_STAC
 1:      movb %al,(%_ASM_CX)
         xor %eax,%eax
         EXIT
@@ -50,6 +53,7 @@ ENTRY(__put_user_2)
         sub $1,%_ASM_BX
         cmp %_ASM_BX,%_ASM_CX
         jae bad_put_user
+        ASM_STAC
 2:      movw %ax,(%_ASM_CX)
         xor %eax,%eax
         EXIT
@@ -61,6 +65,7 @@ ENTRY(__put_user_4)
         sub $3,%_ASM_BX
         cmp %_ASM_BX,%_ASM_CX
         jae bad_put_user
+        ASM_STAC
 3:      movl %eax,(%_ASM_CX)
         xor %eax,%eax
         EXIT
@@ -72,6 +77,7 @@ ENTRY(__put_user_8)
         sub $7,%_ASM_BX
         cmp %_ASM_BX,%_ASM_CX
         jae bad_put_user
+        ASM_STAC
 4:      mov %_ASM_AX,(%_ASM_CX)
 #ifdef CONFIG_X86_32
 5:      movl %edx,4(%_ASM_CX)