xref: /openbmc/linux/include/linux/nospec.h (revision 74e19ef0)
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