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
9 #include <linux/compiler.h>
10 #include <asm/barrier.h>
11
12 struct task_struct;
13
14 /**
15 * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
16 * @index: array element index
17 * @size: number of elements in array
18 *
19 * When @index is out of bounds (@index >= @size), the sign bit will be
20 * set. Extend the sign bit to all bits and invert, giving a result of
21 * zero for an out of bounds index, or ~0 if within bounds [0, @size).
22 */
23 #ifndef array_index_mask_nospec
array_index_mask_nospec(unsigned long index,unsigned long size)24 static inline unsigned long array_index_mask_nospec(unsigned long index,
25 unsigned long size)
26 {
27 /*
28 * Always calculate and emit the mask even if the compiler
29 * thinks the mask is not needed. The compiler does not take
30 * into account the value of @index under speculation.
31 */
32 OPTIMIZER_HIDE_VAR(index);
33 return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
34 }
35 #endif
36
37 /*
38 * array_index_nospec - sanitize an array index after a bounds check
39 *
40 * For a code sequence like:
41 *
42 * if (index < size) {
43 * index = array_index_nospec(index, size);
44 * val = array[index];
45 * }
46 *
47 * ...if the CPU speculates past the bounds check then
48 * array_index_nospec() will clamp the index within the range of [0,
49 * size).
50 */
51 #define array_index_nospec(index, size) \
52 ({ \
53 typeof(index) _i = (index); \
54 typeof(size) _s = (size); \
55 unsigned long _mask = array_index_mask_nospec(_i, _s); \
56 \
57 BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
58 BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
59 \
60 (typeof(_i)) (_i & _mask); \
61 })
62
63 /* Speculation control prctl */
64 int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
65 int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
66 unsigned long ctrl);
67 /* Speculation control for seccomp enforced mitigation */
68 void arch_seccomp_spec_mitigate(struct task_struct *task);
69
70 #endif /* _LINUX_NOSPEC_H */
71