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