73 lines
2.2 KiB
C
73 lines
2.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
// Copyright(c) 2018 Linus Torvalds. All rights reserved.
|
|
// Copyright(c) 2018 Alexei Starovoitov. All rights reserved.
|
|
// Copyright(c) 2018 Intel Corporation. All rights reserved.
|
|
|
|
#ifndef _LINUX_NOSPEC_H
|
|
#define _LINUX_NOSPEC_H
|
|
|
|
/**
|
|
* array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
|
|
* @index: array element index
|
|
* @size: number of elements in array
|
|
*
|
|
* When @index is out of bounds (@index >= @size), the sign bit will be
|
|
* set. Extend the sign bit to all bits and invert, giving a result of
|
|
* zero for an out of bounds index, or ~0 if within bounds [0, @size).
|
|
*/
|
|
#ifndef array_index_mask_nospec
|
|
static inline unsigned long array_index_mask_nospec(unsigned long index,
|
|
unsigned long size)
|
|
{
|
|
/*
|
|
* Warn developers about inappropriate array_index_nospec() usage.
|
|
*
|
|
* Even if the CPU speculates past the WARN_ONCE branch, the
|
|
* sign bit of @index is taken into account when generating the
|
|
* mask.
|
|
*
|
|
* This warning is compiled out when the compiler can infer that
|
|
* @index and @size are less than LONG_MAX.
|
|
*/
|
|
if (WARN_ONCE(index > LONG_MAX || size > LONG_MAX,
|
|
"array_index_nospec() limited to range of [0, LONG_MAX]\n"))
|
|
return 0;
|
|
|
|
/*
|
|
* Always calculate and emit the mask even if the compiler
|
|
* thinks the mask is not needed. The compiler does not take
|
|
* into account the value of @index under speculation.
|
|
*/
|
|
OPTIMIZER_HIDE_VAR(index);
|
|
return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
|
|
}
|
|
#endif
|
|
|
|
/*
|
|
* array_index_nospec - sanitize an array index after a bounds check
|
|
*
|
|
* For a code sequence like:
|
|
*
|
|
* if (index < size) {
|
|
* index = array_index_nospec(index, size);
|
|
* val = array[index];
|
|
* }
|
|
*
|
|
* ...if the CPU speculates past the bounds check then
|
|
* array_index_nospec() will clamp the index within the range of [0,
|
|
* size).
|
|
*/
|
|
#define array_index_nospec(index, size) \
|
|
({ \
|
|
typeof(index) _i = (index); \
|
|
typeof(size) _s = (size); \
|
|
unsigned long _mask = array_index_mask_nospec(_i, _s); \
|
|
\
|
|
BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
|
|
BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
|
|
\
|
|
_i &= _mask; \
|
|
_i; \
|
|
})
|
|
#endif /* _LINUX_NOSPEC_H */
|