library/platform_util.c

/*
 * Common and shared functions used by multiple modules in the Mbed TLS
 * library.
 *
 *  Copyright The Mbed TLS Contributors
 *  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.
 */

/*
 * Ensure gmtime_r is available even with -std=c99; must be defined before
 * config.h, which pulls in glibc's features.h. Harmless on other platforms.
 */
#if !defined(_POSIX_C_SOURCE)
#define _POSIX_C_SOURCE 200112L
#endif

#include "common.h"

#include "mbedtls/platform_util.h"
#include "mbedtls/platform.h"
#include "mbedtls/threading.h"

#include <stddef.h>
#include <string.h>

#if !defined(MBEDTLS_PLATFORM_ZEROIZE_ALT)
/*
 * 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 );
 *
 * Note that it is extremely difficult to guarantee that
 * mbedtls_platform_zeroize() will not be optimized out by aggressive compilers
 * in a portable way. For this reason, Mbed TLS also provides the configuration
 * option MBEDTLS_PLATFORM_ZEROIZE_ALT, which allows users to configure
 * mbedtls_platform_zeroize() to use a suitable implementation for their
 * platform and needs.
 */
static void *(*const volatile memset_func)(void *, int, size_t) = memset;

void mbedtls_platform_zeroize(void *buf, size_t len)
{
    MBEDTLS_INTERNAL_VALIDATE(len == 0 || buf != NULL);

    if (len > 0) {
        memset_func(buf, 0, len);
    }
}
#endif /* MBEDTLS_PLATFORM_ZEROIZE_ALT */

#if defined(MBEDTLS_HAVE_TIME_DATE) && !defined(MBEDTLS_PLATFORM_GMTIME_R_ALT)
#include <time.h>
#if !defined(_WIN32) && (defined(unix) || \
    defined(__unix) || defined(__unix__) || (defined(__APPLE__) && \
    defined(__MACH__)))
#include <unistd.h>
#endif /* !_WIN32 && (unix || __unix || __unix__ ||
        * (__APPLE__ && __MACH__)) */

#if !((defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L) ||     \
    (defined(_POSIX_THREAD_SAFE_FUNCTIONS) &&                     \
    _POSIX_THREAD_SAFE_FUNCTIONS >= 200112L))
/*
 * This is a convenience shorthand macro to avoid checking the long
 * preprocessor conditions above. Ideally, we could expose this macro in
 * platform_util.h and simply use it in platform_util.c, threading.c and
 * threading.h. However, this macro is not part of the Mbed TLS public API, so
 * we keep it private by only defining it in this file
 */
#if !(defined(_WIN32) && !defined(EFIX64) && !defined(EFI32))
#define PLATFORM_UTIL_USE_GMTIME
#endif /* ! ( defined(_WIN32) && !defined(EFIX64) && !defined(EFI32) ) */

#endif /* !( ( defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L ) || \
             ( defined(_POSIX_THREAD_SAFE_FUNCTIONS ) && \
                _POSIX_THREAD_SAFE_FUNCTIONS >= 200112L ) ) */

struct tm *mbedtls_platform_gmtime_r(const mbedtls_time_t *tt,
                                     struct tm *tm_buf)
{
#if defined(_WIN32) && !defined(EFIX64) && !defined(EFI32)
    return (gmtime_s(tm_buf, tt) == 0) ? tm_buf : NULL;
#elif !defined(PLATFORM_UTIL_USE_GMTIME)
    return gmtime_r(tt, tm_buf);
#else
    struct tm *lt;

#if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_lock(&mbedtls_threading_gmtime_mutex) != 0) {
        return NULL;
    }
#endif /* MBEDTLS_THREADING_C */

    lt = gmtime(tt);

    if (lt != NULL) {
        memcpy(tm_buf, lt, sizeof(struct tm));
    }

#if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_unlock(&mbedtls_threading_gmtime_mutex) != 0) {
        return NULL;
    }
#endif /* MBEDTLS_THREADING_C */

    return (lt == NULL) ? NULL : tm_buf;
#endif /* _WIN32 && !EFIX64 && !EFI32 */
}
#endif /* MBEDTLS_HAVE_TIME_DATE && MBEDTLS_PLATFORM_GMTIME_R_ALT */