[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 <asm/barrier.h>

/**
 * 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);					\
})
#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
eb6174f6	8	#include <asm/barrier.h>
f3804203 DW	9
	10	/**
	11	* array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
	12	* @index: array element index
	13	* @size: number of elements in array
	14	*
	15	* When @index is out of bounds (@index >= @size), the sign bit will be
	16	* set. Extend the sign bit to all bits and invert, giving a result of
	17	* zero for an out of bounds index, or ~0 if within bounds [0, @size).
	18	*/
	19	#ifndef array_index_mask_nospec
	20	static inline unsigned long array_index_mask_nospec(unsigned long index,
	21	unsigned long size)
	22	{
f3804203 DW	23	/*
	24	* Always calculate and emit the mask even if the compiler
	25	* thinks the mask is not needed. The compiler does not take
	26	* into account the value of @index under speculation.
	27	*/
	28	OPTIMIZER_HIDE_VAR(index);
	29	return ~(long)(index \| (size - 1UL - index)) >> (BITS_PER_LONG - 1);
	30	}
	31	#endif
	32
	33	/*
	34	* array_index_nospec - sanitize an array index after a bounds check
	35	*
	36	* For a code sequence like:
	37	*
	38	* if (index < size) {
	39	* index = array_index_nospec(index, size);
	40	* val = array[index];
	41	* }
	42	*
	43	* ...if the CPU speculates past the bounds check then
	44	* array_index_nospec() will clamp the index within the range of [0,
	45	* size).
	46	*/
	47	#define array_index_nospec(index, size) \
	48	({ \
	49	typeof(index) _i = (index); \
	50	typeof(size) _s = (size); \
1d91c1d2	51	unsigned long _mask = array_index_mask_nospec(_i, _s); \
f3804203 DW	52	\
	53	BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
	54	BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
	55	\
b98c6a16	56	(typeof(_i)) (_i & _mask); \
f3804203 DW	57	})
f3804203 DW	58	#endif /* _LINUX_NOSPEC_H */