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 #ifndef barrier_nospec
13 # define barrier_nospec() do { } while (0)
14 #endif
15
16 /**
17 * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
18 * @index: array element index
19 * @size: number of elements in array
20 *
21 * When @index is out of bounds (@index >= @size), the sign bit will be
22 * set. Extend the sign bit to all bits and invert, giving a result of
23 * zero for an out of bounds index, or ~0 if within bounds [0, @size).
24 */
25 #ifndef array_index_mask_nospec
array_index_mask_nospec(unsigned long index,unsigned long size)26 static inline unsigned long array_index_mask_nospec(unsigned long index,
27 unsigned long size)
28 {
29 /*
30 * Always calculate and emit the mask even if the compiler
31 * thinks the mask is not needed. The compiler does not take
32 * into account the value of @index under speculation.
33 */
34 OPTIMIZER_HIDE_VAR(index);
35 return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
36 }
37 #endif
38
39 /*
40 * array_index_nospec - sanitize an array index after a bounds check
41 *
42 * For a code sequence like:
43 *
44 * if (index < size) {
45 * index = array_index_nospec(index, size);
46 * val = array[index];
47 * }
48 *
49 * ...if the CPU speculates past the bounds check then
50 * array_index_nospec() will clamp the index within the range of [0,
51 * size).
52 */
53 #define array_index_nospec(index, size) \
54 ({ \
55 typeof(index) _i = (index); \
56 typeof(size) _s = (size); \
57 unsigned long _mask = array_index_mask_nospec(_i, _s); \
58 \
59 BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
60 BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
61 \
62 (typeof(_i)) (_i & _mask); \
63 })
64
65 /* Speculation control prctl */
66 int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
67 int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
68 unsigned long ctrl);
69 /* Speculation control for seccomp enforced mitigation */
70 void arch_seccomp_spec_mitigate(struct task_struct *task);
71
72 #endif /* _LINUX_NOSPEC_H */
73