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

5 files changed, 46 insertions, 28 deletions

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index 75f4c6d..0fe1358 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -126,8 +126,9 @@ static inline int fxsave_user(struct i387_fxsave_struct __user *fx)
 
 	/* See comment in fxsave() below. */
 #ifdef CONFIG_AS_FXSAVEQ
-	asm volatile("1:  fxsaveq %[fx]\n\t"
-		     "2:\n"
+	asm volatile(ASM_STAC "\n"
+		     "1:  fxsaveq %[fx]\n\t"
+		     "2: " ASM_CLAC "\n"
 		     ".section .fixup,\"ax\"\n"
 		     "3:  movl $-1,%[err]\n"
 		     "    jmp  2b\n"
@@ -136,8 +137,9 @@ static inline int fxsave_user(struct i387_fxsave_struct __user *fx)
 		     : [err] "=r" (err), [fx] "=m" (*fx)
 		     : "0" (0));
 #else
-	asm volatile("1:  rex64/fxsave (%[fx])\n\t"
-		     "2:\n"
+	asm volatile(ASM_STAC "\n"
+		     "1:  rex64/fxsave (%[fx])\n\t"
+		     "2: " ASM_CLAC "\n"
 		     ".section .fixup,\"ax\"\n"
 		     "3:  movl $-1,%[err]\n"
 		     "    jmp  2b\n"
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 @@ static inline int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 	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"
diff --git a/arch/x86/include/asm/smap.h b/arch/x86/include/asm/smap.h
index 3989c24..8d3120f 100644
--- a/arch/x86/include/asm/smap.h
+++ b/arch/x86/include/asm/smap.h
@@ -58,13 +58,13 @@
 
 #ifdef CONFIG_X86_SMAP
 
-static inline void clac(void)
+static __always_inline void clac(void)
 {
 	/* Note: a barrier is implicit in alternative() */
 	alternative(ASM_NOP3, __stringify(__ASM_CLAC), X86_FEATURE_SMAP);
 }
 
-static inline void stac(void)
+static __always_inline void stac(void)
 {
 	/* Note: a barrier is implicit in alternative() */
 	alternative(ASM_NOP3, __stringify(__ASM_STAC), X86_FEATURE_SMAP);
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 2c7df3d..b92ece1 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -9,6 +9,7 @@
 #include <linux/string.h>
 #include <asm/asm.h>
 #include <asm/page.h>
+#include <asm/smap.h>
 
 #define VERIFY_READ 0
 #define VERIFY_WRITE 1
@@ -192,9 +193,10 @@ extern int __get_user_bad(void);
 
 #ifdef CONFIG_X86_32
 #define __put_user_asm_u64(x, addr, err, errret)			\
-	asm volatile("1:	movl %%eax,0(%2)\n"			\
+	asm volatile(ASM_STAC "\n"					\
+		     "1:	movl %%eax,0(%2)\n"			\
 		     "2:	movl %%edx,4(%2)\n"			\
-		     "3:\n"						\
+		     "3: " ASM_CLAC "\n"				\
 		     ".section .fixup,\"ax\"\n"				\
 		     "4:	movl %3,%0\n"				\
 		     "	jmp 3b\n"					\
@@ -205,9 +207,10 @@ extern int __get_user_bad(void);
 		     : "A" (x), "r" (addr), "i" (errret), "0" (err))
 
 #define __put_user_asm_ex_u64(x, addr)					\
-	asm volatile("1:	movl %%eax,0(%1)\n"			\
+	asm volatile(ASM_STAC "\n"					\
+		     "1:	movl %%eax,0(%1)\n"			\
 		     "2:	movl %%edx,4(%1)\n"			\
-		     "3:\n"						\
+		     "3: " ASM_CLAC "\n"				\
 		     _ASM_EXTABLE_EX(1b, 2b)				\
 		     _ASM_EXTABLE_EX(2b, 3b)				\
 		     : : "A" (x), "r" (addr))
@@ -379,8 +382,9 @@ do {									\
 } while (0)
 
 #define __get_user_asm(x, addr, err, itype, rtype, ltype, errret)	\
-	asm volatile("1:	mov"itype" %2,%"rtype"1\n"		\
-		     "2:\n"						\
+	asm volatile(ASM_STAC "\n"					\
+		     "1:	mov"itype" %2,%"rtype"1\n"		\
+		     "2: " ASM_CLAC "\n"				\
 		     ".section .fixup,\"ax\"\n"				\
 		     "3:	mov %3,%0\n"				\
 		     "	xor"itype" %"rtype"1,%"rtype"1\n"		\
@@ -412,8 +416,9 @@ do {									\
 } while (0)
 
 #define __get_user_asm_ex(x, addr, itype, rtype, ltype)			\
-	asm volatile("1:	mov"itype" %1,%"rtype"0\n"		\
-		     "2:\n"						\
+	asm volatile(ASM_STAC "\n"					\
+		     "1:	mov"itype" %1,%"rtype"0\n"		\
+		     "2: " ASM_CLAC "\n"				\
 		     _ASM_EXTABLE_EX(1b, 2b)				\
 		     : ltype(x) : "m" (__m(addr)))
 
@@ -443,8 +448,9 @@ struct __large_struct { unsigned long buf[100]; };
  * aliasing issues.
  */
 #define __put_user_asm(x, addr, err, itype, rtype, ltype, errret)	\
-	asm volatile("1:	mov"itype" %"rtype"1,%2\n"		\
-		     "2:\n"						\
+	asm volatile(ASM_STAC "\n"					\
+		     "1:	mov"itype" %"rtype"1,%2\n"		\
+		     "2: " ASM_CLAC "\n"				\
 		     ".section .fixup,\"ax\"\n"				\
 		     "3:	mov %3,%0\n"				\
 		     "	jmp 2b\n"					\
@@ -454,8 +460,9 @@ struct __large_struct { unsigned long buf[100]; };
 		     : ltype(x), "m" (__m(addr)), "i" (errret), "0" (err))
 
 #define __put_user_asm_ex(x, addr, itype, rtype, ltype)			\
-	asm volatile("1:	mov"itype" %"rtype"0,%1\n"		\
-		     "2:\n"						\
+	asm volatile(ASM_STAC "\n"					\
+		     "1:	mov"itype" %"rtype"0,%1\n"		\
+		     "2: " ASM_CLAC "\n"				\
 		     _ASM_EXTABLE_EX(1b, 2b)				\
 		     : : ltype(x), "m" (__m(addr)))
 
diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h
index 8a1b6f9..2a923bd 100644
--- a/arch/x86/include/asm/xsave.h
+++ b/arch/x86/include/asm/xsave.h
@@ -74,8 +74,9 @@ static inline int xsave_user(struct xsave_struct __user *buf)
 	if (unlikely(err))
 		return -EFAULT;
 
-	__asm__ __volatile__("1: .byte " REX_PREFIX "0x0f,0xae,0x27\n"
-			     "2:\n"
+	__asm__ __volatile__(ASM_STAC "\n"
+			     "1: .byte " REX_PREFIX "0x0f,0xae,0x27\n"
+			     "2: " ASM_CLAC "\n"
 			     ".section .fixup,\"ax\"\n"
 			     "3:  movl $-1,%[err]\n"
 			     "    jmp  2b\n"
@@ -97,8 +98,9 @@ static inline int xrestore_user(struct xsave_struct __user *buf, u64 mask)
 	u32 lmask = mask;
 	u32 hmask = mask >> 32;
 
-	__asm__ __volatile__("1: .byte " REX_PREFIX "0x0f,0xae,0x2f\n"
-			     "2:\n"
+	__asm__ __volatile__(ASM_STAC "\n"
+			     "1: .byte " REX_PREFIX "0x0f,0xae,0x2f\n"
+			     "2: " ASM_CLAC "\n"
 			     ".section .fixup,\"ax\"\n"
 			     "3:  movl $-1,%[err]\n"
 			     "    jmp  2b\n"