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
12struct 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
24static 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 */
64int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
65int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
66			     unsigned long ctrl);
67/* Speculation control for seccomp enforced mitigation */
68void arch_seccomp_spec_mitigate(struct task_struct *task);
69
70#endif /* _LINUX_NOSPEC_H */