diff options
Diffstat (limited to 'arch/x86/include/asm/smap.h')
| -rw-r--r-- | arch/x86/include/asm/smap.h | 92 |
1 files changed, 54 insertions, 38 deletions
diff --git a/arch/x86/include/asm/smap.h b/arch/x86/include/asm/smap.h index d17b39893b79..977bef14a0ab 100644 --- a/arch/x86/include/asm/smap.h +++ b/arch/x86/include/asm/smap.h @@ -13,41 +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 CONFIG_X86_SMAP +#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 /* CONFIG_X86_SMAP */ +#else /* __ASSEMBLER__ */ -#define ASM_CLAC -#define ASM_STAC +/* + * 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(). + */ -#endif /* CONFIG_X86_SMAP */ +static __always_inline void clac(void) +{ + alternative("", "clac", X86_FEATURE_SMAP); +} -#else /* __ASSEMBLY__ */ +static __always_inline void stac(void) +{ + alternative("", "stac", X86_FEATURE_SMAP); +} -#ifdef CONFIG_X86_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 clac(void) +static __always_inline void lass_clac(void) { - /* Note: a barrier is implicit in alternative() */ - alternative("", __ASM_CLAC, X86_FEATURE_SMAP); + alternative("", "clac", X86_FEATURE_LASS); } -static __always_inline void stac(void) +static __always_inline void lass_stac(void) { - /* Note: a barrier is implicit in alternative() */ - alternative("", __ASM_STAC, X86_FEATURE_SMAP); + alternative("", "stac", X86_FEATURE_LASS); } static __always_inline unsigned long smap_save(void) @@ -55,7 +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"); @@ -65,30 +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) - -#else /* CONFIG_X86_SMAP */ - -static inline void clac(void) { } -static inline void stac(void) { } - -static inline unsigned long smap_save(void) { return 0; } -static inline void smap_restore(unsigned long flags) { } - -#define ASM_CLAC -#define ASM_STAC + ALTERNATIVE("", "stac", X86_FEATURE_SMAP) -#endif /* CONFIG_X86_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 */ |