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
   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 */
  71