git.zerfleddert.de Git - proxmark3-svn/blob - common/mbedtls/platform_util.c

   1 /*
   2  * Common and shared functions used by multiple modules in the Mbed TLS
   3  * library.
   4  *
   5  *  Copyright (C) 2018, Arm Limited, All Rights Reserved
   6  *  SPDX-License-Identifier: GPL-2.0
   7  *
   8  *  This program is free software; you can redistribute it and/or modify
   9  *  it under the terms of the GNU General Public License as published by
  10  *  the Free Software Foundation; either version 2 of the License, or
  11  *  (at your option) any later version.
  12  *
  13  *  This program is distributed in the hope that it will be useful,
  14  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  *  GNU General Public License for more details.
  17  *
  18  *  You should have received a copy of the GNU General Public License along
  19  *  with this program; if not, write to the Free Software Foundation, Inc.,
  20  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  21  *
  22  *  This file is part of Mbed TLS (https://tls.mbed.org)
  23  */
  24
  25 #if !defined(MBEDTLS_CONFIG_FILE)
  26 #include "mbedtls/config.h"
  27 #else
  28 #include MBEDTLS_CONFIG_FILE
  29 #endif
  30
  31 #include "mbedtls/platform_util.h"
  32
  33 #include <stddef.h>
  34 #include <string.h>
  35
  36 #if !defined(MBEDTLS_PLATFORM_ZEROIZE_ALT)
  37 /*
  38  * This implementation should never be optimized out by the compiler
  39  *
  40  * This implementation for mbedtls_platform_zeroize() was inspired from Colin
  41  * Percival's blog article at:
  42  *
  43  * http://www.daemonology.net/blog/2014-09-04-how-to-zero-a-buffer.html
  44  *
  45  * It uses a volatile function pointer to the standard memset(). Because the
  46  * pointer is volatile the compiler expects it to change at
  47  * any time and will not optimize out the call that could potentially perform
  48  * other operations on the input buffer instead of just setting it to 0.
  49  * Nevertheless, as pointed out by davidtgoldblatt on Hacker News
  50  * (refer to http://www.daemonology.net/blog/2014-09-05-erratum.html for
  51  * details), optimizations of the following form are still possible:
  52  *
  53  * if( memset_func != memset )
  54  *     memset_func( buf, 0, len );
  55  *
  56  * Note that it is extremely difficult to guarantee that
  57  * mbedtls_platform_zeroize() will not be optimized out by aggressive compilers
  58  * in a portable way. For this reason, Mbed TLS also provides the configuration
  59  * option MBEDTLS_PLATFORM_ZEROIZE_ALT, which allows users to configure
  60  * mbedtls_platform_zeroize() to use a suitable implementation for their
  61  * platform and needs.
  62  */
  63 static void * (* const volatile memset_func)( void *, int, size_t ) = memset;
  64
  65 void mbedtls_platform_zeroize( void *buf, size_t len )
  66 {
  67     memset_func( buf, 0, len );
  68 }
  69 #endif /* MBEDTLS_PLATFORM_ZEROIZE_ALT */