| | 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 */ |
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