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 #ifndef barrier_nospec
15 # define barrier_nospec() do { } while (0)
16 #endif
17
18 /**
19 * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
20 * @index: array element index
21 * @size: number of elements in array
22 *
23 * When @index is out of bounds (@index >= @size), the sign bit will be
24 * set. Extend the sign bit to all bits and invert, giving a result of
25 * zero for an out of bounds index, or ~0 if within bounds [0, @size).
26 */
27 #ifndef array_index_mask_nospec
array_index_mask_nospec(unsigned long index,unsigned long size)28 static inline unsigned long array_index_mask_nospec(unsigned long index,
29 unsigned long size)
30 {
31 /*
32 * Always calculate and emit the mask even if the compiler
33 * thinks the mask is not needed. The compiler does not take
34 * into account the value of @index under speculation.
35 */
36 OPTIMIZER_HIDE_VAR(index);
37 return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
38 }
39 #endif
40
41 /*
42 * array_index_nospec - sanitize an array index after a bounds check
43 *
44 * For a code sequence like:
45 *
46 * if (index < size) {
47 * index = array_index_nospec(index, size);
48 * val = array[index];
49 * }
50 *
51 * ...if the CPU speculates past the bounds check then
52 * array_index_nospec() will clamp the index within the range of [0,
53 * size).
54 */
55 #define array_index_nospec(index, size) \
56 ({ \
57 typeof(index) _i = (index); \
58 typeof(size) _s = (size); \
59 unsigned long _mask = array_index_mask_nospec(_i, _s); \
60 \
61 BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
62 BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
63 \
64 (typeof(_i)) (_i & _mask); \
65 })
66
67 /* Speculation control prctl */
68 int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
69 int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
70 unsigned long ctrl);
71 /* Speculation control for seccomp enforced mitigation */
72 void arch_seccomp_spec_mitigate(struct task_struct *task);
73
74 #endif /* _LINUX_NOSPEC_H */
75