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70 lines
2.6 KiB
C
70 lines
2.6 KiB
C
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/*
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* Common and shared functions used by multiple modules in the Mbed TLS
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* library.
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*
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* Copyright (C) 2018, Arm Limited, All Rights Reserved
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* SPDX-License-Identifier: GPL-2.0
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* This file is part of Mbed TLS (https://tls.mbed.org)
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*/
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#if !defined(MBEDTLS_CONFIG_FILE)
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#include "mbedtls/config.h"
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#else
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#include MBEDTLS_CONFIG_FILE
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#endif
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#include "mbedtls/platform_util.h"
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#include <stddef.h>
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#include <string.h>
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#if !defined(MBEDTLS_PLATFORM_ZEROIZE_ALT)
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/*
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* This implementation should never be optimized out by the compiler
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*
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* This implementation for mbedtls_platform_zeroize() was inspired from Colin
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* Percival's blog article at:
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*
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* http://www.daemonology.net/blog/2014-09-04-how-to-zero-a-buffer.html
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*
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* It uses a volatile function pointer to the standard memset(). Because the
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* pointer is volatile the compiler expects it to change at
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* any time and will not optimize out the call that could potentially perform
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* other operations on the input buffer instead of just setting it to 0.
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* Nevertheless, as pointed out by davidtgoldblatt on Hacker News
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* (refer to http://www.daemonology.net/blog/2014-09-05-erratum.html for
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* details), optimizations of the following form are still possible:
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*
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* if( memset_func != memset )
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* memset_func( buf, 0, len );
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*
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* Note that it is extremely difficult to guarantee that
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* mbedtls_platform_zeroize() will not be optimized out by aggressive compilers
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* in a portable way. For this reason, Mbed TLS also provides the configuration
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* option MBEDTLS_PLATFORM_ZEROIZE_ALT, which allows users to configure
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* mbedtls_platform_zeroize() to use a suitable implementation for their
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* platform and needs.
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*/
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static void * (* const volatile memset_func)( void *, int, size_t ) = memset;
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void mbedtls_platform_zeroize( void *buf, size_t len )
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{
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memset_func( buf, 0, len );
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}
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#endif /* MBEDTLS_PLATFORM_ZEROIZE_ALT */
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