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