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/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 69babd8..ce87e3d 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -56,6 +56,7 @@
#include <asm/ftrace.h>
#include <asm/percpu.h>
#include <asm/asm.h>
+#include <asm/smap.h>
#include <linux/err.h>
/* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this. */
@@ -465,7 +466,8 @@
* System call entry. Up to 6 arguments in registers are supported.
*
* SYSCALL does not save anything on the stack and does not change the
- * stack pointer.
+ * stack pointer. However, it does mask the flags register for us, so
+ * CLD and CLAC are not needed.
*/
/*
@@ -884,6 +886,7 @@
*/
.p2align CONFIG_X86_L1_CACHE_SHIFT
common_interrupt:
+ ASM_CLAC
XCPT_FRAME
addq $-0x80,(%rsp) /* Adjust vector to [-256,-1] range */
interrupt do_IRQ
@@ -1023,6 +1026,7 @@
*/
.macro apicinterrupt num sym do_sym
ENTRY(\sym)
+ ASM_CLAC
INTR_FRAME
pushq_cfi $~(\num)
.Lcommon_\sym:
@@ -1077,6 +1081,7 @@
*/
.macro zeroentry sym do_sym
ENTRY(\sym)
+ ASM_CLAC
INTR_FRAME
PARAVIRT_ADJUST_EXCEPTION_FRAME
pushq_cfi $-1 /* ORIG_RAX: no syscall to restart */
@@ -1094,6 +1099,7 @@
.macro paranoidzeroentry sym do_sym
ENTRY(\sym)
+ ASM_CLAC
INTR_FRAME
PARAVIRT_ADJUST_EXCEPTION_FRAME
pushq_cfi $-1 /* ORIG_RAX: no syscall to restart */
@@ -1112,6 +1118,7 @@
#define INIT_TSS_IST(x) PER_CPU_VAR(init_tss) + (TSS_ist + ((x) - 1) * 8)
.macro paranoidzeroentry_ist sym do_sym ist
ENTRY(\sym)
+ ASM_CLAC
INTR_FRAME
PARAVIRT_ADJUST_EXCEPTION_FRAME
pushq_cfi $-1 /* ORIG_RAX: no syscall to restart */
@@ -1131,6 +1138,7 @@
.macro errorentry sym do_sym
ENTRY(\sym)
+ ASM_CLAC
XCPT_FRAME
PARAVIRT_ADJUST_EXCEPTION_FRAME
subq $ORIG_RAX-R15, %rsp
@@ -1149,6 +1157,7 @@
/* error code is on the stack already */
.macro paranoiderrorentry sym do_sym
ENTRY(\sym)
+ ASM_CLAC
XCPT_FRAME
PARAVIRT_ADJUST_EXCEPTION_FRAME
subq $ORIG_RAX-R15, %rsp