8fa80c503b
For architectures providing their own implementation of array_index_mask_nospec() in asm/barrier.h, attempting to use WARN_ONCE() to complain about out-of-range parameters using WARN_ON() results in a mess of mutually-dependent include files. Rather than unpick the dependencies, simply have the core code in nospec.h perform the checking for us. Signed-off-by: Will Deacon <will.deacon@arm.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1517840166-15399-1-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
79 lines
2.4 KiB
C
79 lines
2.4 KiB
C
// SPDX-License-Identifier: GPL-2.0
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// Copyright(c) 2018 Linus Torvalds. All rights reserved.
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// Copyright(c) 2018 Alexei Starovoitov. All rights reserved.
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// Copyright(c) 2018 Intel Corporation. All rights reserved.
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#ifndef _LINUX_NOSPEC_H
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#define _LINUX_NOSPEC_H
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/**
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* array_index_mask_nospec() - generate a ~0 mask when index < size, 0 otherwise
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* @index: array element index
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* @size: number of elements in array
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*
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* When @index is out of bounds (@index >= @size), the sign bit will be
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* set. Extend the sign bit to all bits and invert, giving a result of
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* zero for an out of bounds index, or ~0 if within bounds [0, @size).
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*/
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#ifndef array_index_mask_nospec
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static inline unsigned long array_index_mask_nospec(unsigned long index,
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unsigned long size)
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{
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/*
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* Always calculate and emit the mask even if the compiler
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* thinks the mask is not needed. The compiler does not take
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* into account the value of @index under speculation.
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*/
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OPTIMIZER_HIDE_VAR(index);
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return ~(long)(index | (size - 1UL - index)) >> (BITS_PER_LONG - 1);
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}
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#endif
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/*
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* Warn developers about inappropriate array_index_nospec() usage.
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*
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* Even if the CPU speculates past the WARN_ONCE branch, the
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* sign bit of @index is taken into account when generating the
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* mask.
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*
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* This warning is compiled out when the compiler can infer that
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* @index and @size are less than LONG_MAX.
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*/
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#define array_index_mask_nospec_check(index, size) \
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({ \
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if (WARN_ONCE(index > LONG_MAX || size > LONG_MAX, \
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"array_index_nospec() limited to range of [0, LONG_MAX]\n")) \
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_mask = 0; \
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else \
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_mask = array_index_mask_nospec(index, size); \
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_mask; \
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})
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/*
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* array_index_nospec - sanitize an array index after a bounds check
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*
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* For a code sequence like:
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*
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* if (index < size) {
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* index = array_index_nospec(index, size);
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* val = array[index];
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* }
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*
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* ...if the CPU speculates past the bounds check then
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* array_index_nospec() will clamp the index within the range of [0,
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* size).
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*/
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#define array_index_nospec(index, size) \
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({ \
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typeof(index) _i = (index); \
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typeof(size) _s = (size); \
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unsigned long _mask = array_index_mask_nospec_check(_i, _s); \
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\
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BUILD_BUG_ON(sizeof(_i) > sizeof(long)); \
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BUILD_BUG_ON(sizeof(_s) > sizeof(long)); \
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\
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_i &= _mask; \
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_i; \
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})
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#endif /* _LINUX_NOSPEC_H */
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