/*

 * Constant-time equality testing of memory regions.

 *

 * Authors:

 *

 *   James Yonan <james@openvpn.net>

 *   Daniel Borkmann <dborkman@redhat.com>

 *

 * This file is provided under a dual BSD/GPLv2 license.  When using or

 * redistributing this file, you may do so under either license.

 *

 * GPL LICENSE SUMMARY

 *

 * Copyright(c) 2013 OpenVPN Technologies, Inc. All rights reserved.

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of version 2 of the GNU General Public License as

 * published by the Free Software Foundation.

 *

 * This program is distributed in the hope that it will be useful, but

 * WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.

 * The full GNU General Public License is included in this distribution

 * in the file called LICENSE.GPL.

 *

 * BSD LICENSE

 *

 * Copyright(c) 2013 OpenVPN Technologies, Inc. All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 *   * Redistributions of source code must retain the above copyright

 *     notice, this list of conditions and the following disclaimer.

 *   * Redistributions in binary form must reproduce the above copyright

 *     notice, this list of conditions and the following disclaimer in

 *     the documentation and/or other materials provided with the

 *     distribution.

 *   * Neither the name of OpenVPN Technologies nor the names of its

 *     contributors may be used to endorse or promote products derived

 *     from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

#include <common.h>

#include <crypto.h>

/* Compare two areas of memory without leaking timing information,

 * and with special optimizations for common sizes.  Users should

 * not call this function directly, but should instead use

 * crypto_memneq defined in crypto/algapi.h.

 */

noinline unsigned long __crypto_memneq(const void *a, const void *b,

               size_t size)

{

  unsigned long neq = 0;

#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)

  while (size >= sizeof(unsigned long)) {

    neq |= *(unsigned long *)a ^ *(unsigned long *)b;

    OPTIMIZER_HIDE_VAR(neq);

    a += sizeof(unsigned long);

    b += sizeof(unsigned long);

    size -= sizeof(unsigned long);

  }

#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */

  while (size > 0) {

    neq |= *(unsigned char *)a ^ *(unsigned char *)b;

    OPTIMIZER_HIDE_VAR(neq);

    a += 1;

    b += 1;

    size -= 1;

  }

  return neq;

}