linux/arch/x86/lib/getuser.S
H. Peter Anvin 63bcff2a30 x86, smap: Add STAC and CLAC instructions to control user space access
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
2012-09-21 12:45:27 -07:00

113 lines
2.2 KiB
ArmAsm

/*
* __get_user functions.
*
* (C) Copyright 1998 Linus Torvalds
* (C) Copyright 2005 Andi Kleen
* (C) Copyright 2008 Glauber Costa
*
* These functions have a non-standard call interface
* to make them more efficient, especially as they
* return an error value in addition to the "real"
* return value.
*/
/*
* __get_user_X
*
* Inputs: %[r|e]ax contains the address.
* The register is modified, but all changes are undone
* before returning because the C code doesn't know about it.
*
* Outputs: %[r|e]ax is error code (0 or -EFAULT)
* %[r|e]dx contains zero-extended value
*
*
* These functions should not modify any other registers,
* as they get called from within inline assembly.
*/
#include <linux/linkage.h>
#include <asm/dwarf2.h>
#include <asm/page_types.h>
#include <asm/errno.h>
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>
#include <asm/asm.h>
#include <asm/smap.h>
.text
ENTRY(__get_user_1)
CFI_STARTPROC
GET_THREAD_INFO(%_ASM_DX)
cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
ASM_STAC
1: movzb (%_ASM_AX),%edx
xor %eax,%eax
ASM_CLAC
ret
CFI_ENDPROC
ENDPROC(__get_user_1)
ENTRY(__get_user_2)
CFI_STARTPROC
add $1,%_ASM_AX
jc bad_get_user
GET_THREAD_INFO(%_ASM_DX)
cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
ASM_STAC
2: movzwl -1(%_ASM_AX),%edx
xor %eax,%eax
ASM_CLAC
ret
CFI_ENDPROC
ENDPROC(__get_user_2)
ENTRY(__get_user_4)
CFI_STARTPROC
add $3,%_ASM_AX
jc bad_get_user
GET_THREAD_INFO(%_ASM_DX)
cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
ASM_STAC
3: mov -3(%_ASM_AX),%edx
xor %eax,%eax
ASM_CLAC
ret
CFI_ENDPROC
ENDPROC(__get_user_4)
#ifdef CONFIG_X86_64
ENTRY(__get_user_8)
CFI_STARTPROC
add $7,%_ASM_AX
jc bad_get_user
GET_THREAD_INFO(%_ASM_DX)
cmp TI_addr_limit(%_ASM_DX),%_ASM_AX
jae bad_get_user
ASM_STAC
4: movq -7(%_ASM_AX),%_ASM_DX
xor %eax,%eax
ASM_CLAC
ret
CFI_ENDPROC
ENDPROC(__get_user_8)
#endif
bad_get_user:
CFI_STARTPROC
xor %edx,%edx
mov $(-EFAULT),%_ASM_AX
ASM_CLAC
ret
CFI_ENDPROC
END(bad_get_user)
_ASM_EXTABLE(1b,bad_get_user)
_ASM_EXTABLE(2b,bad_get_user)
_ASM_EXTABLE(3b,bad_get_user)
#ifdef CONFIG_X86_64
_ASM_EXTABLE(4b,bad_get_user)
#endif