linux/crypto/memneq.c
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   1/*
   2 * Constant-time equality testing of memory regions.
   3 *
   4 * Authors:
   5 *
   6 *   James Yonan <james@openvpn.net>
   7 *   Daniel Borkmann <dborkman@redhat.com>
   8 *
   9 * This file is provided under a dual BSD/GPLv2 license.  When using or
  10 * redistributing this file, you may do so under either license.
  11 *
  12 * GPL LICENSE SUMMARY
  13 *
  14 * Copyright(c) 2013 OpenVPN Technologies, Inc. All rights reserved.
  15 *
  16 * This program is free software; you can redistribute it and/or modify
  17 * it under the terms of version 2 of the GNU General Public License as
  18 * published by the Free Software Foundation.
  19 *
  20 * This program is distributed in the hope that it will be useful, but
  21 * WITHOUT ANY WARRANTY; without even the implied warranty of
  22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  23 * General Public License for more details.
  24 *
  25 * You should have received a copy of the GNU General Public License
  26 * along with this program; if not, write to the Free Software
  27 * Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
  28 * The full GNU General Public License is included in this distribution
  29 * in the file called LICENSE.GPL.
  30 *
  31 * BSD LICENSE
  32 *
  33 * Copyright(c) 2013 OpenVPN Technologies, Inc. All rights reserved.
  34 *
  35 * Redistribution and use in source and binary forms, with or without
  36 * modification, are permitted provided that the following conditions
  37 * are met:
  38 *
  39 *   * Redistributions of source code must retain the above copyright
  40 *     notice, this list of conditions and the following disclaimer.
  41 *   * Redistributions in binary form must reproduce the above copyright
  42 *     notice, this list of conditions and the following disclaimer in
  43 *     the documentation and/or other materials provided with the
  44 *     distribution.
  45 *   * Neither the name of OpenVPN Technologies nor the names of its
  46 *     contributors may be used to endorse or promote products derived
  47 *     from this software without specific prior written permission.
  48 *
  49 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  50 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  51 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  52 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  53 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  54 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  55 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  56 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  57 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  58 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  59 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  60 */
  61
  62#include <crypto/algapi.h>
  63
  64#ifndef __HAVE_ARCH_CRYPTO_MEMNEQ
  65
  66/* Generic path for arbitrary size */
  67static inline unsigned long
  68__crypto_memneq_generic(const void *a, const void *b, size_t size)
  69{
  70        unsigned long neq = 0;
  71
  72#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
  73        while (size >= sizeof(unsigned long)) {
  74                neq |= *(unsigned long *)a ^ *(unsigned long *)b;
  75                OPTIMIZER_HIDE_VAR(neq);
  76                a += sizeof(unsigned long);
  77                b += sizeof(unsigned long);
  78                size -= sizeof(unsigned long);
  79        }
  80#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
  81        while (size > 0) {
  82                neq |= *(unsigned char *)a ^ *(unsigned char *)b;
  83                OPTIMIZER_HIDE_VAR(neq);
  84                a += 1;
  85                b += 1;
  86                size -= 1;
  87        }
  88        return neq;
  89}
  90
  91/* Loop-free fast-path for frequently used 16-byte size */
  92static inline unsigned long __crypto_memneq_16(const void *a, const void *b)
  93{
  94        unsigned long neq = 0;
  95
  96#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
  97        if (sizeof(unsigned long) == 8) {
  98                neq |= *(unsigned long *)(a)   ^ *(unsigned long *)(b);
  99                OPTIMIZER_HIDE_VAR(neq);
 100                neq |= *(unsigned long *)(a+8) ^ *(unsigned long *)(b+8);
 101                OPTIMIZER_HIDE_VAR(neq);
 102        } else if (sizeof(unsigned int) == 4) {
 103                neq |= *(unsigned int *)(a)    ^ *(unsigned int *)(b);
 104                OPTIMIZER_HIDE_VAR(neq);
 105                neq |= *(unsigned int *)(a+4)  ^ *(unsigned int *)(b+4);
 106                OPTIMIZER_HIDE_VAR(neq);
 107                neq |= *(unsigned int *)(a+8)  ^ *(unsigned int *)(b+8);
 108                OPTIMIZER_HIDE_VAR(neq);
 109                neq |= *(unsigned int *)(a+12) ^ *(unsigned int *)(b+12);
 110                OPTIMIZER_HIDE_VAR(neq);
 111        } else
 112#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
 113        {
 114                neq |= *(unsigned char *)(a)    ^ *(unsigned char *)(b);
 115                OPTIMIZER_HIDE_VAR(neq);
 116                neq |= *(unsigned char *)(a+1)  ^ *(unsigned char *)(b+1);
 117                OPTIMIZER_HIDE_VAR(neq);
 118                neq |= *(unsigned char *)(a+2)  ^ *(unsigned char *)(b+2);
 119                OPTIMIZER_HIDE_VAR(neq);
 120                neq |= *(unsigned char *)(a+3)  ^ *(unsigned char *)(b+3);
 121                OPTIMIZER_HIDE_VAR(neq);
 122                neq |= *(unsigned char *)(a+4)  ^ *(unsigned char *)(b+4);
 123                OPTIMIZER_HIDE_VAR(neq);
 124                neq |= *(unsigned char *)(a+5)  ^ *(unsigned char *)(b+5);
 125                OPTIMIZER_HIDE_VAR(neq);
 126                neq |= *(unsigned char *)(a+6)  ^ *(unsigned char *)(b+6);
 127                OPTIMIZER_HIDE_VAR(neq);
 128                neq |= *(unsigned char *)(a+7)  ^ *(unsigned char *)(b+7);
 129                OPTIMIZER_HIDE_VAR(neq);
 130                neq |= *(unsigned char *)(a+8)  ^ *(unsigned char *)(b+8);
 131                OPTIMIZER_HIDE_VAR(neq);
 132                neq |= *(unsigned char *)(a+9)  ^ *(unsigned char *)(b+9);
 133                OPTIMIZER_HIDE_VAR(neq);
 134                neq |= *(unsigned char *)(a+10) ^ *(unsigned char *)(b+10);
 135                OPTIMIZER_HIDE_VAR(neq);
 136                neq |= *(unsigned char *)(a+11) ^ *(unsigned char *)(b+11);
 137                OPTIMIZER_HIDE_VAR(neq);
 138                neq |= *(unsigned char *)(a+12) ^ *(unsigned char *)(b+12);
 139                OPTIMIZER_HIDE_VAR(neq);
 140                neq |= *(unsigned char *)(a+13) ^ *(unsigned char *)(b+13);
 141                OPTIMIZER_HIDE_VAR(neq);
 142                neq |= *(unsigned char *)(a+14) ^ *(unsigned char *)(b+14);
 143                OPTIMIZER_HIDE_VAR(neq);
 144                neq |= *(unsigned char *)(a+15) ^ *(unsigned char *)(b+15);
 145                OPTIMIZER_HIDE_VAR(neq);
 146        }
 147
 148        return neq;
 149}
 150
 151/* Compare two areas of memory without leaking timing information,
 152 * and with special optimizations for common sizes.  Users should
 153 * not call this function directly, but should instead use
 154 * crypto_memneq defined in crypto/algapi.h.
 155 */
 156noinline unsigned long __crypto_memneq(const void *a, const void *b,
 157                                       size_t size)
 158{
 159        switch (size) {
 160        case 16:
 161                return __crypto_memneq_16(a, b);
 162        default:
 163                return __crypto_memneq_generic(a, b, size);
 164        }
 165}
 166EXPORT_SYMBOL(__crypto_memneq);
 167
 168#endif /* __HAVE_ARCH_CRYPTO_MEMNEQ */
 169
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