nospec.h 2.14 KB
Newer Older
1 2 3 4 5 6 7
// SPDX-License-Identifier: GPL-2.0
// Copyright(c) 2018 Linus Torvalds. All rights reserved.
// Copyright(c) 2018 Alexei Starovoitov. All rights reserved.
// Copyright(c) 2018 Intel Corporation. All rights reserved.

#ifndef _LINUX_NOSPEC_H
#define _LINUX_NOSPEC_H
8
#include <asm/barrier.h>
9

10 11
struct task_struct;

12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52
/**
 * array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
 * @index: array element index
 * @size: number of elements in array
 *
 * When @index is out of bounds (@index >= @size), the sign bit will be
 * set.  Extend the sign bit to all bits and invert, giving a result of
 * zero for an out of bounds index, or ~0 if within bounds [0, @size).
 */
#ifndef array_index_mask_nospec
static inline unsigned long array_index_mask_nospec(unsigned long index,
						    unsigned long size)
{
	/*
	 * Always calculate and emit the mask even if the compiler
	 * thinks the mask is not needed. The compiler does not take
	 * into account the value of @index under speculation.
	 */
	OPTIMIZER_HIDE_VAR(index);
	return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
}
#endif

/*
 * array_index_nospec - sanitize an array index after a bounds check
 *
 * For a code sequence like:
 *
 *     if (index < size) {
 *         index = array_index_nospec(index, size);
 *         val = array[index];
 *     }
 *
 * ...if the CPU speculates past the bounds check then
 * array_index_nospec() will clamp the index within the range of [0,
 * size).
 */
#define array_index_nospec(index, size)					\
({									\
	typeof(index) _i = (index);					\
	typeof(size) _s = (size);					\
53
	unsigned long _mask = array_index_mask_nospec(_i, _s);		\
54 55 56 57
									\
	BUILD_BUG_ON(sizeof(_i) > sizeof(long));			\
	BUILD_BUG_ON(sizeof(_s) > sizeof(long));			\
									\
58
	(typeof(_i)) (_i & _mask);					\
59
})
60 61

/* Speculation control prctl */
62 63 64
int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
			     unsigned long ctrl);
65 66
/* Speculation control for seccomp enforced mitigation */
void arch_seccomp_spec_mitigate(struct task_struct *task);
67

68
#endif /* _LINUX_NOSPEC_H */