Merge remote-tracking branch 'upstream-restricted/pr/421' into development-proposed

include/mbedtls/config.h

@@ -2852,6 +2852,26 @@
  */
 #define MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE
 
+/**
+ * Uncomment the macro to let mbed TLS use your alternate implementation of
+ * mbedtls_platform_zeroize(). This replaces the default implementation in
+ * platform_util.c.
+ *
+ * mbedtls_platform_zeroize() is a widely used function across the library to
+ * zero a block of memory. The implementation is expected to be secure in the
+ * sense that it has been written to prevent the compiler from removing calls
+ * to mbedtls_platform_zeroize() as part of redundant code elimination
+ * optimizations. However, it is difficult to guarantee that calls to
+ * mbedtls_platform_zeroize() will not be optimized by the compiler as older
+ * versions of the C language standards do not provide a secure implementation
+ * of memset(). Therefore, MBEDTLS_PLATFORM_ZEROIZE_ALT enables users to
+ * configure their own implementation of mbedtls_platform_zeroize(), for
+ * example by using directives specific to their compiler, features from newer
+ * C standards (e.g using memset_s() in C11) or calling a secure memset() from
+ * their system (e.g explicit_bzero() in BSD).
+ */
+//#define MBEDTLS_PLATFORM_ZEROIZE_ALT
+
 /* \} name SECTION: Customisation configuration options */
 
 /* Target and application specific configurations */

include/mbedtls/platform_util.h

@@ -0,0 +1,62 @@
+/**
+ * \file platform_util.h
+ *
+ * \brief Common and shared functions used by multiple modules in the Mbed TLS
+ *        library.
+ */
+/*
+ *  Copyright (C) 2018, Arm Limited, All Rights Reserved
+ *  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.
+ *
+ *  This file is part of Mbed TLS (https://tls.mbed.org)
+ */
+#ifndef MBEDTLS_PLATFORM_UTIL_H
+#define MBEDTLS_PLATFORM_UTIL_H
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * \brief       Securely zeroize a buffer
+ *
+ *              The function is meant to wipe the data contained in a buffer so
+ *              that it can no longer be recovered even if the program memory
+ *              is later compromised. Call this function on sensitive data
+ *              stored on the stack before returning from a function, and on
+ *              sensitive data stored on the heap before freeing the heap
+ *              object.
+ *
+ *              It is extremely difficult to guarantee that calls to
+ *              mbedtls_platform_zeroize() are not removed by aggressive
+ *              compiler optimizations in a portable way. For this reason, Mbed
+ *              TLS 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
+ *
+ * \param buf   Buffer to be zeroized
+ * \param len   Length of the buffer in bytes
+ *
+ */
+void mbedtls_platform_zeroize( void *buf, size_t len );
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* MBEDTLS_PLATFORM_UTIL_H */