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 * Warn developers about inappropriate array_index_nospec() usage. 24 * 25 * Even if the CPU speculates past the WARN_ONCE branch, the 26 * sign bit of @index is taken into account when generating the 27 * mask. 28 * 29 * This warning is compiled out when the compiler can infer that 30 * @index and @size are less than LONG_MAX. 31 */ 32 if (WARN_ONCE(index > LONG_MAX || size > LONG_MAX, 33 "array_index_nospec() limited to range of [0, LONG_MAX]\n")) 34 return 0; 35 36 /* 37 * Always calculate and emit the mask even if the compiler 38 * thinks the mask is not needed. The compiler does not take 39 * into account the value of @index under speculation. 40 */ 41 OPTIMIZER_HIDE_VAR(index); 42 return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1); 43 } 44 #endif 45 46 /* 47 * array_index_nospec - sanitize an array index after a bounds check 48 * 49 * For a code sequence like: 50 * 51 * if (index < size) { 52 * index = array_index_nospec(index, size); 53 * val = array[index]; 54 * } 55 * 56 * ...if the CPU speculates past the bounds check then 57 * array_index_nospec() will clamp the index within the range of [0, 58 * size). 59 */ 60 #define array_index_nospec(index, size) \ 61 ({ \ 62 typeof(index) _i = (index); \ 63 typeof(size) _s = (size); \ 64 unsigned long _mask = array_index_mask_nospec(_i, _s); \ 65 \ 66 BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \ 67 BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \ 68 \ 69 _i &= _mask; \ 70 _i; \ 71 }) 72 #endif /* _LINUX_NOSPEC_H */ 73