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Linux/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                 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 */
 92 static 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  */
156 noinline 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 }
166 EXPORT_SYMBOL(__crypto_memneq);
167 
168 #endif /* __HAVE_ARCH_CRYPTO_MEMNEQ */
169 

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