Add programs/test/zeroize.c to test mbedtls_zeroize

The idea is to use the simple program that is expected to be modified
rarely to set a breakpoint in a specific line and check that the
function mbedtls_zeroize() does actually set the buffer to 0 and is not
optimised out by the compiler.

programs/test/zeroize.c

@@ -0,0 +1,91 @@
+/*
+ *  Zeroize demonstration program
+ *
+ *  Copyright (C) 2017, 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)
+ */
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "mbedtls/config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#include <stdio.h>
+
+#if defined(MBEDTLS_PLATFORM_C)
+#include "mbedtls/platform.h"
+#else
+#include <stdlib.h>
+#define mbedtls_printf     printf
+#define MBEDTLS_EXIT_SUCCESS EXIT_SUCCESS
+#define MBEDTLS_EXIT_FAILURE EXIT_FAILURE
+#endif
+
+#include "mbedtls/utils.h"
+
+#define BUFFER_LEN 1024
+
+void usage( void )
+{
+    mbedtls_printf( "Zeroize is a simple program to assist with testing\n" );
+    mbedtls_printf( "the mbedtls_zeroize() function by using the\n" );
+    mbedtls_printf( "debugger. This program takes a file as input and\n" );
+    mbedtls_printf( "prints the first %d characters. Usage:\n\n", BUFFER_LEN );
+    mbedtls_printf( "       zeroize <FILE>\n" );
+}
+
+int main( int argc, char** argv )
+{
+    int exit_code = MBEDTLS_EXIT_FAILURE;
+    FILE * fp;
+    char buf[BUFFER_LEN];
+    char *p = buf;
+    char *end = p + BUFFER_LEN;
+    char c;
+
+    if( argc != 2 )
+    {
+        mbedtls_printf( "This program takes exactly 1 agument\n" );
+        usage();
+        return( exit_code );
+    }
+
+    fp = fopen( argv[1], "r" );
+    if( fp == NULL )
+    {
+        mbedtls_printf( "Could not open file '%s'\n", argv[1] );
+        return( exit_code );
+    }
+
+    while( ( c = fgetc( fp ) ) != EOF && p < end - 1 )
+        *p++ = c;
+    *p = '\0';
+
+    if( p - buf != 0 )
+    {
+        mbedtls_printf( "%s\n", buf );
+        mbedtls_zeroize( buf, sizeof( buf ) );
+        exit_code = MBEDTLS_EXIT_SUCCESS;
+    }
+    else
+        mbedtls_printf( "The file is empty!\n" );
+
+    fclose( fp );
+
+    return( exit_code );
+}