Quelle nospec.h Sprache: C

// SPDX-License-Identifier: GPL-2.0
// Copyright(c) 2018 Linus Torvalds. All rights reserved.
// Copyright(c) 2018 Alexei Starovoitov. All rights reserved.
// Copyright(c) 2018 Intel Corporation. All rights reserved.

#ifndef _LINUX_NOSPEC_H
#define _LINUX_NOSPEC_H

#include <linux/compiler.h>
#include <asm/barrier.h>

struct task_struct;

#ifndef barrier_nospec
# define barrier_nospec() do { } while (0)
#endif

/**
* array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
* @index: array element index
* @size: number of elements in array
*
* When @index is out of bounds (@index >= @size), the sign bit will be
* set.  Extend the sign bit to all bits and invert, giving a result of
* zero for an out of bounds index, or ~0 if within bounds [0, @size).
*/
#ifndef array_index_mask_nospec
static inline unsigned long array_index_mask_nospec(unsigned long index,
          unsigned long size)
{
/*
* Always calculate and emit the mask even if the compiler
* thinks the mask is not needed. The compiler does not take
* into account the value of @index under speculation.
*/
OPTIMIZER_HIDE_VAR(index);
return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
}
#endif

/*
* array_index_nospec - sanitize an array index after a bounds check
*
* For a code sequence like:
*
*     if (index < size) {
*         index = array_index_nospec(index, size);
*         val = array[index];
*     }
*
* ...if the CPU speculates past the bounds check then
* array_index_nospec() will clamp the index within the range of [0,
* size).
*/
#define array_index_nospec(index, size)     \
({         \
typeof(index) _i = (index);     \
typeof(size) _s = (size);     \
unsigned long _mask = array_index_mask_nospec(_i, _s);  \
         \
BUILD_BUG_ON(sizeof(_i) > sizeof(long));   \
BUILD_BUG_ON(sizeof(_s) > sizeof(long));   \
         \
(typeof(_i)) (_i & _mask);     \
})

/* Speculation control prctl */
int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which);
int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
        unsigned long ctrl);
/* Speculation control for seccomp enforced mitigation */
void arch_seccomp_spec_mitigate(struct task_struct *task);

#endif /* _LINUX_NOSPEC_H */

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