1 files changed, 57 insertions, 17 deletions

diff --git a/arch/x86/include/asm/smap.h b/arch/x86/include/asm/smap.h
index bab490379c65..977bef14a0ab 100644
--- a/arch/x86/include/asm/smap.h
+++ b/arch/x86/include/asm/smap.h
@@ -13,30 +13,63 @@
 #include <asm/cpufeatures.h>
 #include <asm/alternative.h>
 
-/* "Raw" instruction opcodes */
-#define __ASM_CLAC	".byte 0x0f,0x01,0xca"
-#define __ASM_STAC	".byte 0x0f,0x01,0xcb"
-
-#ifdef __ASSEMBLY__
+#ifdef __ASSEMBLER__
 
 #define ASM_CLAC \
-	ALTERNATIVE "", __ASM_CLAC, X86_FEATURE_SMAP
+	ALTERNATIVE "", "clac", X86_FEATURE_SMAP
 
 #define ASM_STAC \
-	ALTERNATIVE "", __ASM_STAC, X86_FEATURE_SMAP
+	ALTERNATIVE "", "stac", X86_FEATURE_SMAP
+
+#else /* __ASSEMBLER__ */
 
-#else /* __ASSEMBLY__ */
+/*
+ * The CLAC/STAC instructions toggle the enforcement of
+ * X86_FEATURE_SMAP along with X86_FEATURE_LASS.
+ *
+ * SMAP enforcement is based on the _PAGE_BIT_USER bit in the page
+ * tables. The kernel is not allowed to touch pages with that bit set
+ * unless the AC bit is set.
+ *
+ * Use stac()/clac() when accessing userspace (_PAGE_USER) mappings,
+ * regardless of location.
+ *
+ * Note: a barrier is implicit in alternative().
+ */
 
 static __always_inline void clac(void)
 {
-	/* Note: a barrier is implicit in alternative() */
-	alternative("", __ASM_CLAC, X86_FEATURE_SMAP);
+	alternative("", "clac", X86_FEATURE_SMAP);
 }
 
 static __always_inline void stac(void)
 {
-	/* Note: a barrier is implicit in alternative() */
-	alternative("", __ASM_STAC, X86_FEATURE_SMAP);
+	alternative("", "stac", X86_FEATURE_SMAP);
+}
+
+/*
+ * LASS enforcement is based on bit 63 of the virtual address. The
+ * kernel is not allowed to touch memory in the lower half of the
+ * virtual address space.
+ *
+ * Use lass_stac()/lass_clac() to toggle the AC bit for kernel data
+ * accesses (!_PAGE_USER) that are blocked by LASS, but not by SMAP.
+ *
+ * Even with the AC bit set, LASS will continue to block instruction
+ * fetches from the user half of the address space. To allow those,
+ * clear CR4.LASS to disable the LASS mechanism entirely.
+ *
+ * Note: a barrier is implicit in alternative().
+ */
+
+static __always_inline void lass_clac(void)
+{
+	alternative("", "clac", X86_FEATURE_LASS);
+}
+
+static __always_inline void lass_stac(void)
+{
+	alternative("", "stac", X86_FEATURE_LASS);
 }
 
 static __always_inline unsigned long smap_save(void)
@@ -44,7 +77,8 @@ static __always_inline unsigned long smap_save(void)
 	unsigned long flags;
 
 	asm volatile ("# smap_save\n\t"
-		      ALTERNATIVE("", "pushf; pop %0; " __ASM_CLAC "\n\t",
+		      ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE "\n\t"
+				  "", "pushf; pop %0; clac",
 				  X86_FEATURE_SMAP)
 		      : "=rm" (flags) : : "memory", "cc");
 
@@ -54,17 +88,23 @@ static __always_inline unsigned long smap_save(void)
 static __always_inline void smap_restore(unsigned long flags)
 {
 	asm volatile ("# smap_restore\n\t"
-		      ALTERNATIVE("", "push %0; popf\n\t",
+		      ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE "\n\t"
+				  "", "push %0; popf",
 				  X86_FEATURE_SMAP)
 		      : : "g" (flags) : "memory", "cc");
 }
 
 /* These macros can be used in asm() statements */
 #define ASM_CLAC \
-	ALTERNATIVE("", __ASM_CLAC, X86_FEATURE_SMAP)
+	ALTERNATIVE("", "clac", X86_FEATURE_SMAP)
 #define ASM_STAC \
-	ALTERNATIVE("", __ASM_STAC, X86_FEATURE_SMAP)
+	ALTERNATIVE("", "stac", X86_FEATURE_SMAP)
+
+#define ASM_CLAC_UNSAFE \
+	ALTERNATIVE("", ANNOTATE_IGNORE_ALTERNATIVE "\n\t" "clac", X86_FEATURE_SMAP)
+#define ASM_STAC_UNSAFE \
+	ALTERNATIVE("", ANNOTATE_IGNORE_ALTERNATIVE "\n\t" "stac", X86_FEATURE_SMAP)
 
-#endif /* __ASSEMBLY__ */
+#endif /* __ASSEMBLER__ */
 
 #endif /* _ASM_X86_SMAP_H */