lib/crypto/memneq.c

   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 <linux/unaligned.h>
  63 #include <crypto/algapi.h>
  64 #include <linux/module.h>
  65
  66 /* Generic path for arbitrary size */
  67 static 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 |= get_unaligned((unsigned long *)a) ^
  75                        get_unaligned((unsigned long *)b);
  76                 OPTIMIZER_HIDE_VAR(neq);
  77                 a += sizeof(unsigned long);
  78                 b += sizeof(unsigned long);
  79                 size -= sizeof(unsigned long);
  80         }
  81 #endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
  82         while (size > 0) {
  83                 neq |= *(unsigned char *)a ^ *(unsigned char *)b;
  84                 OPTIMIZER_HIDE_VAR(neq);
  85                 a += 1;
  86                 b += 1;
  87                 size -= 1;
  88         }
  89         return neq;
  90 }
  91
  92 /* Loop-free fast-path for frequently used 16-byte size */
  93 static inline unsigned long __crypto_memneq_16(const void *a, const void *b)
  94 {
  95         unsigned long neq = 0;
  96
  97 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
  98         if (sizeof(unsigned long) == 8) {
  99                 neq |= get_unaligned((unsigned long *)a) ^
 100                        get_unaligned((unsigned long *)b);
 101                 OPTIMIZER_HIDE_VAR(neq);
 102                 neq |= get_unaligned((unsigned long *)(a + 8)) ^
 103                        get_unaligned((unsigned long *)(b + 8));
 104                 OPTIMIZER_HIDE_VAR(neq);
 105         } else if (sizeof(unsigned int) == 4) {
 106                 neq |= get_unaligned((unsigned int *)a) ^
 107                        get_unaligned((unsigned int *)b);
 108                 OPTIMIZER_HIDE_VAR(neq);
 109                 neq |= get_unaligned((unsigned int *)(a + 4)) ^
 110                        get_unaligned((unsigned int *)(b + 4));
 111                 OPTIMIZER_HIDE_VAR(neq);
 112                 neq |= get_unaligned((unsigned int *)(a + 8)) ^
 113                        get_unaligned((unsigned int *)(b + 8));
 114                 OPTIMIZER_HIDE_VAR(neq);
 115                 neq |= get_unaligned((unsigned int *)(a + 12)) ^
 116                        get_unaligned((unsigned int *)(b + 12));
 117                 OPTIMIZER_HIDE_VAR(neq);
 118         } else
 119 #endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
 120         {
 121                 neq |= *(unsigned char *)(a)    ^ *(unsigned char *)(b);
 122                 OPTIMIZER_HIDE_VAR(neq);
 123                 neq |= *(unsigned char *)(a+1)  ^ *(unsigned char *)(b+1);
 124                 OPTIMIZER_HIDE_VAR(neq);
 125                 neq |= *(unsigned char *)(a+2)  ^ *(unsigned char *)(b+2);
 126                 OPTIMIZER_HIDE_VAR(neq);
 127                 neq |= *(unsigned char *)(a+3)  ^ *(unsigned char *)(b+3);
 128                 OPTIMIZER_HIDE_VAR(neq);
 129                 neq |= *(unsigned char *)(a+4)  ^ *(unsigned char *)(b+4);
 130                 OPTIMIZER_HIDE_VAR(neq);
 131                 neq |= *(unsigned char *)(a+5)  ^ *(unsigned char *)(b+5);
 132                 OPTIMIZER_HIDE_VAR(neq);
 133                 neq |= *(unsigned char *)(a+6)  ^ *(unsigned char *)(b+6);
 134                 OPTIMIZER_HIDE_VAR(neq);
 135                 neq |= *(unsigned char *)(a+7)  ^ *(unsigned char *)(b+7);
 136                 OPTIMIZER_HIDE_VAR(neq);
 137                 neq |= *(unsigned char *)(a+8)  ^ *(unsigned char *)(b+8);
 138                 OPTIMIZER_HIDE_VAR(neq);
 139                 neq |= *(unsigned char *)(a+9)  ^ *(unsigned char *)(b+9);
 140                 OPTIMIZER_HIDE_VAR(neq);
 141                 neq |= *(unsigned char *)(a+10) ^ *(unsigned char *)(b+10);
 142                 OPTIMIZER_HIDE_VAR(neq);
 143                 neq |= *(unsigned char *)(a+11) ^ *(unsigned char *)(b+11);
 144                 OPTIMIZER_HIDE_VAR(neq);
 145                 neq |= *(unsigned char *)(a+12) ^ *(unsigned char *)(b+12);
 146                 OPTIMIZER_HIDE_VAR(neq);
 147                 neq |= *(unsigned char *)(a+13) ^ *(unsigned char *)(b+13);
 148                 OPTIMIZER_HIDE_VAR(neq);
 149                 neq |= *(unsigned char *)(a+14) ^ *(unsigned char *)(b+14);
 150                 OPTIMIZER_HIDE_VAR(neq);
 151                 neq |= *(unsigned char *)(a+15) ^ *(unsigned char *)(b+15);
 152                 OPTIMIZER_HIDE_VAR(neq);
 153         }
 154
 155         return neq;
 156 }
 157
 158 /* Compare two areas of memory without leaking timing information,
 159  * and with special optimizations for common sizes.  Users should
 160  * not call this function directly, but should instead use
 161  * crypto_memneq defined in crypto/algapi.h.
 162  */
 163 noinline unsigned long __crypto_memneq(const void *a, const void *b,
 164                                        size_t size)
 165 {
 166         switch (size) {
 167         case 16:
 168                 return __crypto_memneq_16(a, b);
 169         default:
 170                 return __crypto_memneq_generic(a, b, size);
 171         }
 172 }
 173 EXPORT_SYMBOL(__crypto_memneq);