1 // SPDX-License-Identifier: GPL-2.0
2 // Copyright(c) 2018 Linus Torvalds. All rights reserved.
3 // Copyright(c) 2018 Alexei Starovoitov. All rights reserved.
4 // Copyright(c) 2018 Intel Corporation. All rights reserved.
6 #ifndef _LINUX_NOSPEC_H
7 #define _LINUX_NOSPEC_H
10 * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
11 * @index: array element index
12 * @size: number of elements in array
14 * When @index is out of bounds (@index >= @size), the sign bit will be
15 * set. Extend the sign bit to all bits and invert, giving a result of
16 * zero for an out of bounds index, or ~0 if within bounds [0, @size).
18 #ifndef array_index_mask_nospec
19 static inline unsigned long array_index_mask_nospec(unsigned long index,
23 * Always calculate and emit the mask even if the compiler
24 * thinks the mask is not needed. The compiler does not take
25 * into account the value of @index under speculation.
27 OPTIMIZER_HIDE_VAR(index);
28 return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
33 * array_index_nospec - sanitize an array index after a bounds check
35 * For a code sequence like:
38 * index = array_index_nospec(index, size);
42 * ...if the CPU speculates past the bounds check then
43 * array_index_nospec() will clamp the index within the range of [0,
46 #define array_index_nospec(index, size) \
48 typeof(index) _i = (index); \
49 typeof(size) _s = (size); \
50 unsigned long _mask = array_index_mask_nospec(_i, _s); \
52 BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
53 BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
58 #endif /* _LINUX_NOSPEC_H */