diff options
Diffstat (limited to 'arch/x86/include/asm/smap.h')
| -rw-r--r-- | arch/x86/include/asm/smap.h | 129 |
1 files changed, 74 insertions, 55 deletions
diff --git a/arch/x86/include/asm/smap.h b/arch/x86/include/asm/smap.h index 8d3120f4e270..977bef14a0ab 100644 --- a/arch/x86/include/asm/smap.h +++ b/arch/x86/include/asm/smap.h @@ -1,91 +1,110 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ /* * Supervisor Mode Access Prevention support * * Copyright (C) 2012 Intel Corporation * Author: H. Peter Anvin <hpa@linux.intel.com> - * - * This program is free software; you can redistribute it and/or - * modify it under the terms of the GNU General Public License - * as published by the Free Software Foundation; version 2 - * of the License. */ #ifndef _ASM_X86_SMAP_H #define _ASM_X86_SMAP_H -#include <linux/stringify.h> #include <asm/nops.h> -#include <asm/cpufeature.h> +#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 __ASSEMBLER__ -#ifdef __ASSEMBLY__ +#define ASM_CLAC \ + ALTERNATIVE "", "clac", X86_FEATURE_SMAP -#include <asm/alternative-asm.h> +#define ASM_STAC \ + ALTERNATIVE "", "stac", X86_FEATURE_SMAP -#ifdef CONFIG_X86_SMAP +#else /* __ASSEMBLER__ */ -#define ASM_CLAC \ - 661: ASM_NOP3 ; \ - .pushsection .altinstr_replacement, "ax" ; \ - 662: __ASM_CLAC ; \ - .popsection ; \ - .pushsection .altinstructions, "a" ; \ - altinstruction_entry 661b, 662b, X86_FEATURE_SMAP, 3, 3 ; \ - .popsection +/* + * 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(). + */ -#define ASM_STAC \ - 661: ASM_NOP3 ; \ - .pushsection .altinstr_replacement, "ax" ; \ - 662: __ASM_STAC ; \ - .popsection ; \ - .pushsection .altinstructions, "a" ; \ - altinstruction_entry 661b, 662b, X86_FEATURE_SMAP, 3, 3 ; \ - .popsection +static __always_inline void clac(void) +{ + alternative("", "clac", X86_FEATURE_SMAP); +} -#else /* CONFIG_X86_SMAP */ +static __always_inline void stac(void) +{ + alternative("", "stac", X86_FEATURE_SMAP); +} -#define ASM_CLAC -#define ASM_STAC +/* + * 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(). + */ -#endif /* CONFIG_X86_SMAP */ +static __always_inline void lass_clac(void) +{ + alternative("", "clac", X86_FEATURE_LASS); +} -#else /* __ASSEMBLY__ */ +static __always_inline void lass_stac(void) +{ + alternative("", "stac", X86_FEATURE_LASS); +} -#include <asm/alternative.h> +static __always_inline unsigned long smap_save(void) +{ + unsigned long flags; -#ifdef CONFIG_X86_SMAP + asm volatile ("# smap_save\n\t" + ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE "\n\t" + "", "pushf; pop %0; clac", + X86_FEATURE_SMAP) + : "=rm" (flags) : : "memory", "cc"); -static __always_inline void clac(void) -{ - /* Note: a barrier is implicit in alternative() */ - alternative(ASM_NOP3, __stringify(__ASM_CLAC), X86_FEATURE_SMAP); + return flags; } -static __always_inline void stac(void) +static __always_inline void smap_restore(unsigned long flags) { - /* Note: a barrier is implicit in alternative() */ - alternative(ASM_NOP3, __stringify(__ASM_STAC), X86_FEATURE_SMAP); + asm volatile ("# smap_restore\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_NOP3, __stringify(__ASM_CLAC), X86_FEATURE_SMAP) + ALTERNATIVE("", "clac", X86_FEATURE_SMAP) #define ASM_STAC \ - ALTERNATIVE(ASM_NOP3, __stringify(__ASM_STAC), X86_FEATURE_SMAP) - -#else /* CONFIG_X86_SMAP */ - -static inline void clac(void) { } -static inline void stac(void) { } - -#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 */ |