nospec.h (2216B)
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 */