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 struct task_struct;
11
12 /**
13 * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
14 * @index: array element index
15 * @size: number of elements in array
16 *
17 * When @index is out of bounds (@index >= @size), the sign bit will be
18 * set. Extend the sign bit to all bits and invert, giving a result of
19 * zero for an out of bounds index, or ~0 if within bounds [0, @size).
20 */
21 #ifndef array_index_mask_nospec
22 static inline unsigned long array_index_mask_nospec(unsigned long index,
23 unsigned long size)
24 {
25 /*
26 * Always calculate and emit the mask even if the compiler
27 * thinks the mask is not needed. The compiler does not take
28 * into account the value of @index under speculation.
29 */
30 OPTIMIZER_HIDE_VAR(index);
31 return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
32 }
33 #endif
34
35 /*
36 * array_index_nospec - sanitize an array index after a bounds check
37 *
38 * For a code sequence like:
39 *
40 * if (index < size) {
41 * index = array_index_nospec(index, size);
42 * val = array[index];
43 * }
44 *
45 * ...if the CPU speculates past the bounds check then
46 * array_index_nospec() will clamp the index within the range of [0,
47 * size).
48 */
49 #define array_index_nospec(index, size) \
50 ({ \
51 typeof(index) _i = (index); \
52 typeof(size) _s = (size); \
53 unsigned long _mask = array_index_mask_nospec(_i, _s); \
54 \
55 BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
56 BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
57 \
58 (typeof(_i)) (_i & _mask); \
59 })
60
61 /* Speculation control prctl */
62 int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
63 int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
64 unsigned long ctrl);
65 /* Speculation control for seccomp enforced mitigation */
66 void arch_seccomp_spec_mitigate(struct task_struct *task);
67
68 #endif /* _LINUX_NOSPEC_H */