[linux-block.git] / include / linux / nospec.h

// 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;

/**
 * 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 */
Commit	Line	Data
f3804203 DW	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
002dff36 WD	8
002dff36 WD	9	#include <linux/compiler.h>
eb6174f6	10	#include <asm/barrier.h>
f3804203	11
7bbf1373 KC	12	struct task_struct;
7bbf1373 KC	13
f3804203 DW	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	{
f3804203 DW	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); \
1d91c1d2	55	unsigned long _mask = array_index_mask_nospec(_i, _s); \
f3804203 DW	56	\
	57	BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
	58	BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
	59	\
b98c6a16	60	(typeof(_i)) (_i & _mask); \
f3804203	61	})
b617cfc8 TG	62
b617cfc8 TG	63	/* Speculation control prctl */
7bbf1373 KC	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);
8bf37d8c TG	67	/* Speculation control for seccomp enforced mitigation */
8bf37d8c TG	68	void arch_seccomp_spec_mitigate(struct task_struct *task);
b617cfc8	69
f3804203	70	#endif /* _LINUX_NOSPEC_H */