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/include/asm/futex.h b/arch/x86/include/asm/futex.h
index 71ecbcb..f373046 100644
--- a/arch/x86/include/asm/futex.h
+++ b/arch/x86/include/asm/futex.h
@@ -9,10 +9,13 @@
#include <asm/asm.h>
#include <asm/errno.h>
#include <asm/processor.h>
+#include <asm/smap.h>
#define __futex_atomic_op1(insn, ret, oldval, uaddr, oparg) \
- asm volatile("1:\t" insn "\n" \
- "2:\t.section .fixup,\"ax\"\n" \
+ asm volatile("\t" ASM_STAC "\n" \
+ "1:\t" insn "\n" \
+ "2:\t" ASM_CLAC "\n" \
+ "\t.section .fixup,\"ax\"\n" \
"3:\tmov\t%3, %1\n" \
"\tjmp\t2b\n" \
"\t.previous\n" \
@@ -21,12 +24,14 @@
: "i" (-EFAULT), "0" (oparg), "1" (0))
#define __futex_atomic_op2(insn, ret, oldval, uaddr, oparg) \
- asm volatile("1:\tmovl %2, %0\n" \
+ asm volatile("\t" ASM_STAC "\n" \
+ "1:\tmovl %2, %0\n" \
"\tmovl\t%0, %3\n" \
"\t" insn "\n" \
"2:\t" LOCK_PREFIX "cmpxchgl %3, %2\n" \
"\tjnz\t1b\n" \
- "3:\t.section .fixup,\"ax\"\n" \
+ "3:\t" ASM_CLAC "\n" \
+ "\t.section .fixup,\"ax\"\n" \
"4:\tmov\t%5, %1\n" \
"\tjmp\t3b\n" \
"\t.previous\n" \
@@ -122,8 +127,10 @@
if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
return -EFAULT;
- asm volatile("1:\t" LOCK_PREFIX "cmpxchgl %4, %2\n"
- "2:\t.section .fixup, \"ax\"\n"
+ asm volatile("\t" ASM_STAC "\n"
+ "1:\t" LOCK_PREFIX "cmpxchgl %4, %2\n"
+ "2:\t" ASM_CLAC "\n"
+ "\t.section .fixup, \"ax\"\n"
"3:\tmov %3, %0\n"
"\tjmp 2b\n"
"\t.previous\n"