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.
5
6 #ifndef _LINUX_NOSPEC_H
7 #define _LINUX_NOSPEC_H
8 #include <asm/barrier.h>
9
10 /**
11 * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
12 * @index: array element index
13 * @size: number of elements in array
14 *
15 * When @index is out of bounds (@index >= @size), the sign bit will be
16 * set. Extend the sign bit to all bits and invert, giving a result of
17 * zero for an out of bounds index, or ~0 if within bounds [0, @size).
18 */
19 #ifndef array_index_mask_nospec
array_index_mask_nospec(unsigned long index,unsigned long size)20 static inline unsigned long array_index_mask_nospec(unsigned long index,
21 unsigned long size)
22 {
23 /*
24 * Always calculate and emit the mask even if the compiler
25 * thinks the mask is not needed. The compiler does not take
26 * into account the value of @index under speculation.
27 */
28 OPTIMIZER_HIDE_VAR(index);
29 return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
30 }
31 #endif
32
33 /*
34 * array_index_nospec - sanitize an array index after a bounds check
35 *
36 * For a code sequence like:
37 *
38 * if (index < size) {
39 * index = array_index_nospec(index, size);
40 * val = array[index];
41 * }
42 *
43 * ...if the CPU speculates past the bounds check then
44 * array_index_nospec() will clamp the index within the range of [0,
45 * size).
46 */
47 #define array_index_nospec(index, size) \
48 ({ \
49 typeof(index) _i = (index); \
50 typeof(size) _s = (size); \
51 unsigned long _mask = array_index_mask_nospec(_i, _s); \
52 \
53 BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
54 BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
55 \
56 (typeof(_i)) (_i & _mask); \
57 })
58 #endif /* _LINUX_NOSPEC_H */
59