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#include <linux/export.h>
 64#include <linux/module.h>
 65#include <linux/unaligned.h>
 66
 67/* Generic path for arbitrary size */
 68static inline unsigned long
 69__crypto_memneq_generic(const void *a, const void *b, size_t size)
 70{
 71	unsigned long neq = 0;
 72
 73#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
 74	while (size >= sizeof(unsigned long)) {
 75		neq |= get_unaligned((unsigned long *)a) ^
 76		       get_unaligned((unsigned long *)b);
 77		OPTIMIZER_HIDE_VAR(neq);
 78		a += sizeof(unsigned long);
 79		b += sizeof(unsigned long);
 80		size -= sizeof(unsigned long);
 81	}
 82#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
 83	while (size > 0) {
 84		neq |= *(unsigned char *)a ^ *(unsigned char *)b;
 85		OPTIMIZER_HIDE_VAR(neq);
 86		a += 1;
 87		b += 1;
 88		size -= 1;
 89	}
 90	return neq;
 91}
 92
 93/* Loop-free fast-path for frequently used 16-byte size */
 94static inline unsigned long __crypto_memneq_16(const void *a, const void *b)
 95{
 96	unsigned long neq = 0;
 97
 98#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 99	if (sizeof(unsigned long) == 8) {
100		neq |= get_unaligned((unsigned long *)a) ^
101		       get_unaligned((unsigned long *)b);
102		OPTIMIZER_HIDE_VAR(neq);
103		neq |= get_unaligned((unsigned long *)(a + 8)) ^
104		       get_unaligned((unsigned long *)(b + 8));
105		OPTIMIZER_HIDE_VAR(neq);
106	} else if (sizeof(unsigned int) == 4) {
107		neq |= get_unaligned((unsigned int *)a) ^
108		       get_unaligned((unsigned int *)b);
109		OPTIMIZER_HIDE_VAR(neq);
110		neq |= get_unaligned((unsigned int *)(a + 4)) ^
111		       get_unaligned((unsigned int *)(b + 4));
112		OPTIMIZER_HIDE_VAR(neq);
113		neq |= get_unaligned((unsigned int *)(a + 8)) ^
114		       get_unaligned((unsigned int *)(b + 8));
115		OPTIMIZER_HIDE_VAR(neq);
116		neq |= get_unaligned((unsigned int *)(a + 12)) ^
117		       get_unaligned((unsigned int *)(b + 12));
118		OPTIMIZER_HIDE_VAR(neq);
119	} else
120#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
121	{
122		neq |= *(unsigned char *)(a)    ^ *(unsigned char *)(b);
123		OPTIMIZER_HIDE_VAR(neq);
124		neq |= *(unsigned char *)(a+1)  ^ *(unsigned char *)(b+1);
125		OPTIMIZER_HIDE_VAR(neq);
126		neq |= *(unsigned char *)(a+2)  ^ *(unsigned char *)(b+2);
127		OPTIMIZER_HIDE_VAR(neq);
128		neq |= *(unsigned char *)(a+3)  ^ *(unsigned char *)(b+3);
129		OPTIMIZER_HIDE_VAR(neq);
130		neq |= *(unsigned char *)(a+4)  ^ *(unsigned char *)(b+4);
131		OPTIMIZER_HIDE_VAR(neq);
132		neq |= *(unsigned char *)(a+5)  ^ *(unsigned char *)(b+5);
133		OPTIMIZER_HIDE_VAR(neq);
134		neq |= *(unsigned char *)(a+6)  ^ *(unsigned char *)(b+6);
135		OPTIMIZER_HIDE_VAR(neq);
136		neq |= *(unsigned char *)(a+7)  ^ *(unsigned char *)(b+7);
137		OPTIMIZER_HIDE_VAR(neq);
138		neq |= *(unsigned char *)(a+8)  ^ *(unsigned char *)(b+8);
139		OPTIMIZER_HIDE_VAR(neq);
140		neq |= *(unsigned char *)(a+9)  ^ *(unsigned char *)(b+9);
141		OPTIMIZER_HIDE_VAR(neq);
142		neq |= *(unsigned char *)(a+10) ^ *(unsigned char *)(b+10);
143		OPTIMIZER_HIDE_VAR(neq);
144		neq |= *(unsigned char *)(a+11) ^ *(unsigned char *)(b+11);
145		OPTIMIZER_HIDE_VAR(neq);
146		neq |= *(unsigned char *)(a+12) ^ *(unsigned char *)(b+12);
147		OPTIMIZER_HIDE_VAR(neq);
148		neq |= *(unsigned char *)(a+13) ^ *(unsigned char *)(b+13);
149		OPTIMIZER_HIDE_VAR(neq);
150		neq |= *(unsigned char *)(a+14) ^ *(unsigned char *)(b+14);
151		OPTIMIZER_HIDE_VAR(neq);
152		neq |= *(unsigned char *)(a+15) ^ *(unsigned char *)(b+15);
153		OPTIMIZER_HIDE_VAR(neq);
154	}
155
156	return neq;
157}
158
159/* Compare two areas of memory without leaking timing information,
160 * and with special optimizations for common sizes.  Users should
161 * not call this function directly, but should instead use
162 * crypto_memneq defined in crypto/algapi.h.
163 */
164noinline unsigned long __crypto_memneq(const void *a, const void *b,
165				       size_t size)
166{
167	switch (size) {
168	case 16:
169		return __crypto_memneq_16(a, b);
170	default:
171		return __crypto_memneq_generic(a, b, size);
172	}
173}
174EXPORT_SYMBOL(__crypto_memneq);