mem_zeroize.c

/*
 * Clear memory contents.
 * Taken from Mbed TLS/Crypto libraries (platform_utils.c).
 *
 *  Copyright (C) 2018, Arm Limited, All Rights Reserved
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

#include "mem_zeroize.h"
#include <string.h>

/*
 * This implementation should never be optimized out by the compiler
 *
 * This implementation for mbedtls_platform_zeroize() was inspired from Colin
 * Percival's blog article at:
 *
 * http://www.daemonology.net/blog/2014-09-04-how-to-zero-a-buffer.html
 *
 * It uses a volatile function pointer to the standard memset(). Because the
 * pointer is volatile the compiler expects it to change at
 * any time and will not optimize out the call that could potentially perform
 * other operations on the input buffer instead of just setting it to 0.
 * Nevertheless, as pointed out by davidtgoldblatt on Hacker News
 * (refer to http://www.daemonology.net/blog/2014-09-05-erratum.html for
 * details), optimizations of the following form are still possible:
 *
 * if (memset_func != memset)
 *     memset_func(buf, 0, len);
 */
void * (* volatile memset_func)(void *, int, size_t) = memset;


void mem_zeroize(void *buf, size_t len)
{
	memset_func(buf, 0, len);
}