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x86, smap: Add STAC and CLAC instructions to control user space access

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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
This commit is contained in:
H. Peter Anvin
2012-09-21 12:43:12 -07:00
parent a052858fab
commit 63bcff2a30
14 changed files with 106 additions and 32 deletions
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10
arch/x86/include/asm/xsave.h
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@@ -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"