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1c16dfbe6c
The C standard does not support dereferencing pointers that are not aligned with respect to the pointed-to type, and doing so is technically undefined behavior, even if the underlying hardware supports it. This means that conditionally dereferencing such pointers based on whether CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y is not the right thing to do, and actually results in alignment faults on ARM, which are fixed up on a slow path. Instead, we should use the unaligned accessors in such cases: on architectures that don't care about alignment, they will result in identical codegen whereas, e.g., codegen on ARM will avoid doubleword loads and stores but use ordinary ones, which are able to tolerate misalignment. Link: https://lore.kernel.org/linux-crypto/CAHk-=wiKkdYLY0bv+nXrcJz3NH9mAqPAafX7PpW5EwVtxsEu7Q@mail.gmail.com/ Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Arnd Bergmann <arnd@arndb.de> Reviewed-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
176 lines
6.4 KiB
C
176 lines
6.4 KiB
C
/*
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* Constant-time equality testing of memory regions.
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*
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* Authors:
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*
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* James Yonan <james@openvpn.net>
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* Daniel Borkmann <dborkman@redhat.com>
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*
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* This file is provided under a dual BSD/GPLv2 license. When using or
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* redistributing this file, you may do so under either license.
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*
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* GPL LICENSE SUMMARY
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*
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* Copyright(c) 2013 OpenVPN Technologies, Inc. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of version 2 of the GNU General Public License as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
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* The full GNU General Public License is included in this distribution
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* in the file called LICENSE.GPL.
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*
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* BSD LICENSE
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*
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* Copyright(c) 2013 OpenVPN Technologies, Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* * Neither the name of OpenVPN Technologies nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <crypto/algapi.h>
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#include <asm/unaligned.h>
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#ifndef __HAVE_ARCH_CRYPTO_MEMNEQ
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/* Generic path for arbitrary size */
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static inline unsigned long
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__crypto_memneq_generic(const void *a, const void *b, size_t size)
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{
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unsigned long neq = 0;
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#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
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while (size >= sizeof(unsigned long)) {
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neq |= get_unaligned((unsigned long *)a) ^
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get_unaligned((unsigned long *)b);
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OPTIMIZER_HIDE_VAR(neq);
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a += sizeof(unsigned long);
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b += sizeof(unsigned long);
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size -= sizeof(unsigned long);
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}
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#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
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while (size > 0) {
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neq |= *(unsigned char *)a ^ *(unsigned char *)b;
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OPTIMIZER_HIDE_VAR(neq);
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a += 1;
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b += 1;
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size -= 1;
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}
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return neq;
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}
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/* Loop-free fast-path for frequently used 16-byte size */
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static inline unsigned long __crypto_memneq_16(const void *a, const void *b)
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{
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unsigned long neq = 0;
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#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
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if (sizeof(unsigned long) == 8) {
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neq |= get_unaligned((unsigned long *)a) ^
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get_unaligned((unsigned long *)b);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= get_unaligned((unsigned long *)(a + 8)) ^
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get_unaligned((unsigned long *)(b + 8));
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OPTIMIZER_HIDE_VAR(neq);
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} else if (sizeof(unsigned int) == 4) {
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neq |= get_unaligned((unsigned int *)a) ^
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get_unaligned((unsigned int *)b);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= get_unaligned((unsigned int *)(a + 4)) ^
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get_unaligned((unsigned int *)(b + 4));
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OPTIMIZER_HIDE_VAR(neq);
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neq |= get_unaligned((unsigned int *)(a + 8)) ^
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get_unaligned((unsigned int *)(b + 8));
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OPTIMIZER_HIDE_VAR(neq);
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neq |= get_unaligned((unsigned int *)(a + 12)) ^
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get_unaligned((unsigned int *)(b + 12));
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OPTIMIZER_HIDE_VAR(neq);
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} else
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#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
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{
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neq |= *(unsigned char *)(a) ^ *(unsigned char *)(b);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+1) ^ *(unsigned char *)(b+1);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+2) ^ *(unsigned char *)(b+2);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+3) ^ *(unsigned char *)(b+3);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+4) ^ *(unsigned char *)(b+4);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+5) ^ *(unsigned char *)(b+5);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+6) ^ *(unsigned char *)(b+6);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+7) ^ *(unsigned char *)(b+7);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+8) ^ *(unsigned char *)(b+8);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+9) ^ *(unsigned char *)(b+9);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+10) ^ *(unsigned char *)(b+10);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+11) ^ *(unsigned char *)(b+11);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+12) ^ *(unsigned char *)(b+12);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+13) ^ *(unsigned char *)(b+13);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+14) ^ *(unsigned char *)(b+14);
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OPTIMIZER_HIDE_VAR(neq);
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neq |= *(unsigned char *)(a+15) ^ *(unsigned char *)(b+15);
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OPTIMIZER_HIDE_VAR(neq);
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}
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return neq;
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}
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/* Compare two areas of memory without leaking timing information,
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* and with special optimizations for common sizes. Users should
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* not call this function directly, but should instead use
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* crypto_memneq defined in crypto/algapi.h.
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*/
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noinline unsigned long __crypto_memneq(const void *a, const void *b,
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size_t size)
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{
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switch (size) {
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case 16:
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return __crypto_memneq_16(a, b);
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default:
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return __crypto_memneq_generic(a, b, size);
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}
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}
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EXPORT_SYMBOL(__crypto_memneq);
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#endif /* __HAVE_ARCH_CRYPTO_MEMNEQ */
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