platform_util.c

00001 /*
00002  * Common and shared functions used by multiple modules in the Mbed TLS
00003  * library.
00004  *
00005  *  Copyright (C) 2018, Arm Limited, All Rights Reserved
00006  *  SPDX-License-Identifier: Apache-2.0
00007  *
00008  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
00009  *  not use this file except in compliance with the License.
00010  *  You may obtain a copy of the License at
00011  *
00012  *  http://www.apache.org/licenses/LICENSE-2.0
00013  *
00014  *  Unless required by applicable law or agreed to in writing, software
00015  *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
00016  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00017  *  See the License for the specific language governing permissions and
00018  *  limitations under the License.
00019  *
00020  *  This file is part of Mbed TLS (https://tls.mbed.org)
00021  */
00022 
00023 /*
00024  * Ensure gmtime_r is available even with -std=c99; must be defined before
00025  * config.h, which pulls in glibc's features.h. Harmless on other platforms.
00026  */
00027 #if !defined(_POSIX_C_SOURCE)
00028 #define _POSIX_C_SOURCE 200112L
00029 #endif
00030 
00031 #if !defined(MBEDTLS_CONFIG_FILE)
00032 #include "mbedtls/config.h"
00033 #else
00034 #include MBEDTLS_CONFIG_FILE
00035 #endif
00036 
00037 #include "mbedtls/platform_util.h"
00038 #include "mbedtls/platform.h"
00039 #include "mbedtls/threading.h"
00040 
00041 #include <stddef.h>
00042 #include <string.h>
00043 
00044 #if !defined(MBEDTLS_PLATFORM_ZEROIZE_ALT)
00045 /*
00046  * This implementation should never be optimized out by the compiler
00047  *
00048  * This implementation for mbedtls_platform_zeroize() was inspired from Colin
00049  * Percival's blog article at:
00050  *
00051  * http://www.daemonology.net/blog/2014-09-04-how-to-zero-a-buffer.html
00052  *
00053  * It uses a volatile function pointer to the standard memset(). Because the
00054  * pointer is volatile the compiler expects it to change at
00055  * any time and will not optimize out the call that could potentially perform
00056  * other operations on the input buffer instead of just setting it to 0.
00057  * Nevertheless, as pointed out by davidtgoldblatt on Hacker News
00058  * (refer to http://www.daemonology.net/blog/2014-09-05-erratum.html for
00059  * details), optimizations of the following form are still possible:
00060  *
00061  * if( memset_func != memset )
00062  *     memset_func( buf, 0, len );
00063  *
00064  * Note that it is extremely difficult to guarantee that
00065  * mbedtls_platform_zeroize() will not be optimized out by aggressive compilers
00066  * in a portable way. For this reason, Mbed TLS also provides the configuration
00067  * option MBEDTLS_PLATFORM_ZEROIZE_ALT, which allows users to configure
00068  * mbedtls_platform_zeroize() to use a suitable implementation for their
00069  * platform and needs.
00070  */
00071 static void * (* const volatile memset_func)( void *, int, size_t ) = memset;
00072 
00073 void mbedtls_platform_zeroize( void *buf, size_t len )
00074 {
00075     MBEDTLS_INTERNAL_VALIDATE( len == 0 || buf != NULL );
00076 
00077     if( len > 0 )
00078         memset_func( buf, 0, len );
00079 }
00080 #endif /* MBEDTLS_PLATFORM_ZEROIZE_ALT */
00081 
00082 #if defined(MBEDTLS_HAVE_TIME_DATE) && !defined(MBEDTLS_PLATFORM_GMTIME_R_ALT)
00083 #include <time.h>
00084 #if !defined(_WIN32) && (defined(unix) || \
00085     defined(__unix) || defined(__unix__) || (defined(__APPLE__) && \
00086     defined(__MACH__)))
00087 #include <unistd.h>
00088 #endif /* !_WIN32 && (unix || __unix || __unix__ ||
00089         * (__APPLE__ && __MACH__)) */
00090 
00091 #if !( ( defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L ) ||     \
00092        ( defined(_POSIX_THREAD_SAFE_FUNCTIONS ) &&                     \
00093          _POSIX_THREAD_SAFE_FUNCTIONS >= 20112L ) )
00094 /*
00095  * This is a convenience shorthand macro to avoid checking the long
00096  * preprocessor conditions above. Ideally, we could expose this macro in
00097  * platform_util.h and simply use it in platform_util.c, threading.c and
00098  * threading.h. However, this macro is not part of the Mbed TLS public API, so
00099  * we keep it private by only defining it in this file
00100  */
00101 #if ! ( defined(_WIN32) && !defined(EFIX64) && !defined(EFI32) )
00102 #define PLATFORM_UTIL_USE_GMTIME
00103 #endif /* ! ( defined(_WIN32) && !defined(EFIX64) && !defined(EFI32) ) */
00104 
00105 #endif /* !( ( defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L ) ||     \
00106              ( defined(_POSIX_THREAD_SAFE_FUNCTIONS ) &&                     \
00107                 _POSIX_THREAD_SAFE_FUNCTIONS >= 20112L ) ) */
00108 
00109 struct tm *mbedtls_platform_gmtime_r( const mbedtls_time_t *tt,
00110                                       struct tm *tm_buf )
00111 {
00112 #if defined(_WIN32) && !defined(EFIX64) && !defined(EFI32)
00113     return( ( gmtime_s( tm_buf, tt ) == 0 ) ? tm_buf : NULL );
00114 #elif !defined(PLATFORM_UTIL_USE_GMTIME)
00115     return( gmtime_r( tt, tm_buf ) );
00116 #else
00117     struct tm *lt;
00118 
00119 #if defined(MBEDTLS_THREADING_C)
00120     if( mbedtls_mutex_lock( &mbedtls_threading_gmtime_mutex ) != 0 )
00121         return( NULL );
00122 #endif /* MBEDTLS_THREADING_C */
00123 
00124     lt = gmtime( tt );
00125 
00126     if( lt != NULL )
00127     {
00128         memcpy( tm_buf, lt, sizeof( struct tm ) );
00129     }
00130 
00131 #if defined(MBEDTLS_THREADING_C)
00132     if( mbedtls_mutex_unlock( &mbedtls_threading_gmtime_mutex ) != 0 )
00133         return( NULL );
00134 #endif /* MBEDTLS_THREADING_C */
00135 
00136     return( ( lt == NULL ) ? NULL : tm_buf );
00137 #endif /* _WIN32 && !EFIX64 && !EFI32 */
00138 }
00139 #endif /* MBEDTLS_HAVE_TIME_DATE && MBEDTLS_PLATFORM_GMTIME_R_ALT */