LXR linux/include/linux/nospec.h

   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
  10struct 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
  22static 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 */
  62int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
  63int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
  64                             unsigned long ctrl);
  65/* Speculation control for seccomp enforced mitigation */
  66void arch_seccomp_spec_mitigate(struct task_struct *task);
  67
  68#endif /* _LINUX_NOSPEC_H */
  69