Line data    Source code

       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             : 
      12             : struct 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
      24             : static 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           0 :         OPTIMIZER_HIDE_VAR(index);
      33           0 :         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 */
      64             : int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
      65             : int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
      66             :                              unsigned long ctrl);
      67             : /* Speculation control for seccomp enforced mitigation */
      68             : void arch_seccomp_spec_mitigate(struct task_struct *task);
      69             : 
      70             : #endif /* _LINUX_NOSPEC_H */