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x86: Make __get_user() generate an out-of-line call

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Instead of inlining the whole stac/lfence/mov/clac sequence (which also
requires individual exception table entries and several asm instruction
alternatives entries), just generate "call __get_user_nocheck_X" for the
__get_user() cases.

We can use all the same infrastructure that we already do for the
regular "get_user()", and the end result is simpler source code, and
much simpler code generation.

It also means that when I introduce asm goto with input for
"unsafe_get_user()", there are no nasty interactions with the
__get_user() code.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2020-04-08 12:50:01 -07:00
parent 53acd35050
commit ea6f043fc9
2 changed files with 116 additions and 76 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

132
arch/x86/include/asm/uaccess.h
View File

@ -96,25 +96,14 @@ static inline bool pagefault_disabled(void);
likely(!__range_not_ok(addr, size, user_addr_max())); \
})
/*
* These are the main single-value transfer routines. They automatically
* use the right size if we just have the right pointer type.
*
* This gets kind of ugly. We want to return _two_ values in "get_user()"
* and yet we don't want to do any pointers, because that is too much
* of a performance impact. Thus we have a few rather ugly macros here,
* and hide all the ugliness from the user.
*
* The "__xxx" versions of the user access functions are versions that
* do not verify the address space, that must have been done previously
* with a separate "access_ok()" call (this is used when we do multiple
* accesses to the same area of user memory).
*/
extern int __get_user_1(void);
extern int __get_user_2(void);
extern int __get_user_4(void);
extern int __get_user_8(void);
extern int __get_user_nocheck_1(void);
extern int __get_user_nocheck_2(void);
extern int __get_user_nocheck_4(void);
extern int __get_user_nocheck_8(void);
extern int __get_user_bad(void);
#define __uaccess_begin() stac()
@ -138,6 +127,37 @@ extern int __get_user_bad(void);
#define __typefits(x,type,not) \
__builtin_choose_expr(sizeof(x)<=sizeof(type),(unsigned type)0,not)
/*
* This is used for both get_user() and __get_user() to expand to
* the proper special function call that has odd calling conventions
* due to returning both a value and an error, and that depends on
* the size of the pointer passed in.
*
* Careful: we have to cast the result to the type of the pointer
* for sign reasons.
*
* The use of _ASM_DX as the register specifier is a bit of a
* simplification, as gcc only cares about it as the starting point
* and not size: for a 64-bit value it will use %ecx:%edx on 32 bits
* (%ecx being the next register in gcc's x86 register sequence), and
* %rdx on 64 bits.
*
* Clang/LLVM cares about the size of the register, but still wants
* the base register for something that ends up being a pair.
*/
#define do_get_user_call(fn,x,ptr) \
({ \
int __ret_gu; \
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
__chk_user_ptr(ptr); \
asm volatile("call __" #fn "_%P4" \
: "=a" (__ret_gu), "=r" (__val_gu), \
ASM_CALL_CONSTRAINT \
: "0" (ptr), "i" (sizeof(*(ptr)))); \
(x) = (__force __typeof__(*(ptr))) __val_gu; \
__builtin_expect(__ret_gu, 0); \
})
/**
* get_user - Get a simple variable from user space.
* @x: Variable to store result.
@ -156,32 +176,30 @@ extern int __get_user_bad(void);
* Return: zero on success, or -EFAULT on error.
* On error, the variable @x is set to zero.
*/
/*
* Careful: we have to cast the result to the type of the pointer
* for sign reasons.
#define get_user(x,ptr) ({ might_fault(); do_get_user_call(get_user,x,ptr); })
/**
* __get_user - Get a simple variable from user space, with less checking.
* @x: Variable to store result.
* @ptr: Source address, in user space.
*
* The use of _ASM_DX as the register specifier is a bit of a
* simplification, as gcc only cares about it as the starting point
* and not size: for a 64-bit value it will use %ecx:%edx on 32 bits
* (%ecx being the next register in gcc's x86 register sequence), and
* %rdx on 64 bits.
* Context: User context only. This function may sleep if pagefaults are
* enabled.
*
* Clang/LLVM cares about the size of the register, but still wants
* the base register for something that ends up being a pair.
* This macro copies a single simple variable from user space to kernel
* space. It supports simple types like char and int, but not larger
* data types like structures or arrays.
*
* @ptr must have pointer-to-simple-variable type, and the result of
* dereferencing @ptr must be assignable to @x without a cast.
*
* Caller must check the pointer with access_ok() before calling this
* function.
*
* Return: zero on success, or -EFAULT on error.
* On error, the variable @x is set to zero.
*/
#define get_user(x, ptr) \
({ \
int __ret_gu; \
register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX); \
__chk_user_ptr(ptr); \
might_fault(); \
asm volatile("call __get_user_%P4" \
: "=a" (__ret_gu), "=r" (__val_gu), \
ASM_CALL_CONSTRAINT \
: "0" (ptr), "i" (sizeof(*(ptr)))); \
(x) = (__force __typeof__(*(ptr))) __val_gu; \
__builtin_expect(__ret_gu, 0); \
})
#define __get_user(x,ptr) do_get_user_call(get_user_nocheck,x,ptr)
#define __put_user_x(size, x, ptr, __ret_pu) \
asm volatile("call __put_user_" #size : "=a" (__ret_pu) \
@ -367,19 +385,6 @@ __pu_label: \
__builtin_expect(__pu_err, 0); \
})
#define __get_user_nocheck(x, ptr, size) \
({ \
int __gu_err; \
__inttype(*(ptr)) __gu_val; \
__typeof__(ptr) __gu_ptr = (ptr); \
__typeof__(size) __gu_size = (size); \
__uaccess_begin_nospec(); \
__get_user_size(__gu_val, __gu_ptr, __gu_size, __gu_err); \
__uaccess_end(); \
(x) = (__force __typeof__(*(ptr)))__gu_val; \
__builtin_expect(__gu_err, 0); \
})
/* FIXME: this hack is definitely wrong -AK */
struct __large_struct { unsigned long buf[100]; };
#define __m(x) (*(struct __large_struct __user *)(x))
@ -396,31 +401,6 @@ struct __large_struct { unsigned long buf[100]; };
: : ltype(x), "m" (__m(addr)) \
: : label)
/**
* __get_user - Get a simple variable from user space, with less checking.
* @x: Variable to store result.
* @ptr: Source address, in user space.
*
* Context: User context only. This function may sleep if pagefaults are
* enabled.
*
* This macro copies a single simple variable from user space to kernel
* space. It supports simple types like char and int, but not larger
* data types like structures or arrays.
*
* @ptr must have pointer-to-simple-variable type, and the result of
* dereferencing @ptr must be assignable to @x without a cast.
*
* Caller must check the pointer with access_ok() before calling this
* function.
*
* Return: zero on success, or -EFAULT on error.
* On error, the variable @x is set to zero.
*/
#define __get_user(x, ptr) \
__get_user_nocheck((x), (ptr), sizeof(*(ptr)))
/**
* __put_user - Write a simple value into user space, with less checking.
* @x: Value to copy to user space.

60
arch/x86/lib/getuser.S
View File

@ -35,6 +35,8 @@
#include <asm/smap.h>
#include <asm/export.h>
#define ASM_BARRIER_NOSPEC ALTERNATIVE "", "lfence", X86_FEATURE_LFENCE_RDTSC
.text
SYM_FUNC_START(__get_user_1)
mov PER_CPU_VAR(current_task), %_ASM_DX
@ -114,6 +116,52 @@ SYM_FUNC_START(__get_user_8)
SYM_FUNC_END(__get_user_8)
EXPORT_SYMBOL(__get_user_8)
/* .. and the same for __get_user, just without the range checks */
SYM_FUNC_START(__get_user_nocheck_1)
ASM_STAC
ASM_BARRIER_NOSPEC
6: movzbl (%_ASM_AX),%edx
xor %eax,%eax
ASM_CLAC
ret
SYM_FUNC_END(__get_user_nocheck_1)
EXPORT_SYMBOL(__get_user_nocheck_1)
SYM_FUNC_START(__get_user_nocheck_2)
ASM_STAC
ASM_BARRIER_NOSPEC
7: movzwl (%_ASM_AX),%edx
xor %eax,%eax
ASM_CLAC
ret
SYM_FUNC_END(__get_user_nocheck_2)
EXPORT_SYMBOL(__get_user_nocheck_2)
SYM_FUNC_START(__get_user_nocheck_4)
ASM_STAC
ASM_BARRIER_NOSPEC
8: movl (%_ASM_AX),%edx
xor %eax,%eax
ASM_CLAC
ret
SYM_FUNC_END(__get_user_nocheck_4)
EXPORT_SYMBOL(__get_user_nocheck_4)
SYM_FUNC_START(__get_user_nocheck_8)
ASM_STAC
ASM_BARRIER_NOSPEC
#ifdef CONFIG_X86_64
9: movq (%_ASM_AX),%rdx
#else
9: movl (%_ASM_AX),%edx
10: movl 4(%_ASM_AX),%ecx
#endif
xor %eax,%eax
ASM_CLAC
ret
SYM_FUNC_END(__get_user_nocheck_8)
EXPORT_SYMBOL(__get_user_nocheck_8)
SYM_CODE_START_LOCAL(.Lbad_get_user_clac)
ASM_CLAC
@ -134,6 +182,7 @@ bad_get_user_8:
SYM_CODE_END(.Lbad_get_user_8_clac)
#endif
/* get_user */
_ASM_EXTABLE_UA(1b, .Lbad_get_user_clac)
_ASM_EXTABLE_UA(2b, .Lbad_get_user_clac)
_ASM_EXTABLE_UA(3b, .Lbad_get_user_clac)
@ -143,3 +192,14 @@ SYM_CODE_END(.Lbad_get_user_8_clac)
_ASM_EXTABLE_UA(4b, .Lbad_get_user_8_clac)
_ASM_EXTABLE_UA(5b, .Lbad_get_user_8_clac)
#endif
/* __get_user */
_ASM_EXTABLE_UA(6b, .Lbad_get_user_clac)
_ASM_EXTABLE_UA(7b, .Lbad_get_user_clac)
_ASM_EXTABLE_UA(8b, .Lbad_get_user_clac)
#ifdef CONFIG_X86_64
_ASM_EXTABLE_UA(9b, .Lbad_get_user_clac)
#else
_ASM_EXTABLE_UA(9b, .Lbad_get_user_8_clac)
_ASM_EXTABLE_UA(10b, .Lbad_get_user_8_clac)
#endif