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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
92 lines
2.1 KiB
C
92 lines
2.1 KiB
C
/*
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* Supervisor Mode Access Prevention support
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*
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* Copyright (C) 2012 Intel Corporation
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* Author: H. Peter Anvin <hpa@linux.intel.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; version 2
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* of the License.
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*/
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#ifndef _ASM_X86_SMAP_H
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#define _ASM_X86_SMAP_H
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#include <linux/stringify.h>
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#include <asm/nops.h>
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#include <asm/cpufeature.h>
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/* "Raw" instruction opcodes */
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#define __ASM_CLAC .byte 0x0f,0x01,0xca
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#define __ASM_STAC .byte 0x0f,0x01,0xcb
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#ifdef __ASSEMBLY__
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#include <asm/alternative-asm.h>
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#ifdef CONFIG_X86_SMAP
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#define ASM_CLAC \
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661: ASM_NOP3 ; \
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.pushsection .altinstr_replacement, "ax" ; \
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662: __ASM_CLAC ; \
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.popsection ; \
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.pushsection .altinstructions, "a" ; \
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altinstruction_entry 661b, 662b, X86_FEATURE_SMAP, 3, 3 ; \
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.popsection
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#define ASM_STAC \
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661: ASM_NOP3 ; \
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.pushsection .altinstr_replacement, "ax" ; \
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662: __ASM_STAC ; \
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.popsection ; \
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.pushsection .altinstructions, "a" ; \
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altinstruction_entry 661b, 662b, X86_FEATURE_SMAP, 3, 3 ; \
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.popsection
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#else /* CONFIG_X86_SMAP */
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#define ASM_CLAC
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#define ASM_STAC
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#endif /* CONFIG_X86_SMAP */
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#else /* __ASSEMBLY__ */
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#include <asm/alternative.h>
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#ifdef CONFIG_X86_SMAP
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static __always_inline void clac(void)
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{
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/* Note: a barrier is implicit in alternative() */
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alternative(ASM_NOP3, __stringify(__ASM_CLAC), X86_FEATURE_SMAP);
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}
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static __always_inline void stac(void)
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{
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/* Note: a barrier is implicit in alternative() */
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alternative(ASM_NOP3, __stringify(__ASM_STAC), X86_FEATURE_SMAP);
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}
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/* These macros can be used in asm() statements */
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#define ASM_CLAC \
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ALTERNATIVE(ASM_NOP3, __stringify(__ASM_CLAC), X86_FEATURE_SMAP)
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#define ASM_STAC \
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ALTERNATIVE(ASM_NOP3, __stringify(__ASM_STAC), X86_FEATURE_SMAP)
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#else /* CONFIG_X86_SMAP */
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static inline void clac(void) { }
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static inline void stac(void) { }
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#define ASM_CLAC
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#define ASM_STAC
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#endif /* CONFIG_X86_SMAP */
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_X86_SMAP_H */
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