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 <crypto/algapi.h>
  63
  64 #ifndef __HAVE_ARCH_CRYPTO_MEMNEQ
  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 |= *(unsigned long *)a ^ *(unsigned long *)b;
  75                 a += sizeof(unsigned long);
  76                 b += sizeof(unsigned long);
  77                 size -= sizeof(unsigned long);
  78         }
  79 #endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
  80         while (size > 0) {
  81                 neq |= *(unsigned char *)a ^ *(unsigned char *)b;
  82                 a += 1;
  83                 b += 1;
  84                 size -= 1;
  85         }
  86         return neq;
  87 }
  88
  89 /* Loop-free fast-path for frequently used 16-byte size */
  90 static inline unsigned long __crypto_memneq_16(const void *a, const void *b)
  91 {
  92 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
  93         if (sizeof(unsigned long) == 8)
  94                 return ((*(unsigned long *)(a)   ^ *(unsigned long *)(b))
  95                       | (*(unsigned long *)(a+8) ^ *(unsigned long *)(b+8)));
  96         else if (sizeof(unsigned int) == 4)
  97                 return ((*(unsigned int *)(a)    ^ *(unsigned int *)(b))
  98                       | (*(unsigned int *)(a+4)  ^ *(unsigned int *)(b+4))
  99                       | (*(unsigned int *)(a+8)  ^ *(unsigned int *)(b+8))
 100                       | (*(unsigned int *)(a+12) ^ *(unsigned int *)(b+12)));
 101         else
 102 #endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
 103                 return ((*(unsigned char *)(a)    ^ *(unsigned char *)(b))
 104                       | (*(unsigned char *)(a+1)  ^ *(unsigned char *)(b+1))
 105                       | (*(unsigned char *)(a+2)  ^ *(unsigned char *)(b+2))
 106                       | (*(unsigned char *)(a+3)  ^ *(unsigned char *)(b+3))
 107                       | (*(unsigned char *)(a+4)  ^ *(unsigned char *)(b+4))
 108                       | (*(unsigned char *)(a+5)  ^ *(unsigned char *)(b+5))
 109                       | (*(unsigned char *)(a+6)  ^ *(unsigned char *)(b+6))
 110                       | (*(unsigned char *)(a+7)  ^ *(unsigned char *)(b+7))
 111                       | (*(unsigned char *)(a+8)  ^ *(unsigned char *)(b+8))
 112                       | (*(unsigned char *)(a+9)  ^ *(unsigned char *)(b+9))
 113                       | (*(unsigned char *)(a+10) ^ *(unsigned char *)(b+10))
 114                       | (*(unsigned char *)(a+11) ^ *(unsigned char *)(b+11))
 115                       | (*(unsigned char *)(a+12) ^ *(unsigned char *)(b+12))
 116                       | (*(unsigned char *)(a+13) ^ *(unsigned char *)(b+13))
 117                       | (*(unsigned char *)(a+14) ^ *(unsigned char *)(b+14))
 118                       | (*(unsigned char *)(a+15) ^ *(unsigned char *)(b+15)));
 119 }
 120
 121 /* Compare two areas of memory without leaking timing information,
 122  * and with special optimizations for common sizes.  Users should
 123  * not call this function directly, but should instead use
 124  * crypto_memneq defined in crypto/algapi.h.
 125  */
 126 noinline unsigned long __crypto_memneq(const void *a, const void *b,
 127                                        size_t size)
 128 {
 129         switch (size) {
 130         case 16:
 131                 return __crypto_memneq_16(a, b);
 132         default:
 133                 return __crypto_memneq_generic(a, b, size);
 134         }
 135 }
 136 EXPORT_SYMBOL(__crypto_memneq);
 137
 138 #endif /* __HAVE_ARCH_CRYPTO_MEMNEQ */