cd066f3622
commit 1d91c1d2c80cb70e2e553845e278b87a960c04da upstream. There are multiple problems with the dynamic sanity checking in array_index_nospec_mask_check(): * It causes unnecessary overhead in the 32-bit case since integer sized @index values will no longer cause the check to be compiled away like in the 64-bit case. * In the 32-bit case it may trigger with user controllable input when the expectation is that should only trigger during development of new kernel enabling. * The macro reuses the input parameter in multiple locations which is broken if someone passes an expression like 'index++' to array_index_nospec(). Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Cc: linux-arch@vger.kernel.org Link: http://lkml.kernel.org/r/151881604278.17395.6605847763178076520.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Ben Hutchings <ben.hutchings@codethink.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
58 lines
1.8 KiB
C
58 lines
1.8 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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#include <asm/barrier.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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* 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(_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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(typeof(_i)) (_i & _mask); \
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})
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#endif /* _LINUX_NOSPEC_H */
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