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