Add a facility to configure entropy sources

Add a function to configure entropy sources. For testing only.

Use it to test that the library initialization fails properly if there is no
entropy source.

library/psa_crypto.c

@@ -43,6 +43,7 @@
 
 #include "psa/crypto.h"
 
+#include "psa_crypto_invasive.h"
 /* Include internal declarations that are useful for implementing persistently
  * stored keys. */
 #include "psa_crypto_storage.h"
@@ -155,6 +156,8 @@ enum rng_state
 
 typedef struct
 {
+    void (* entropy_init )( mbedtls_entropy_context *ctx );
+    void (* entropy_free )( mbedtls_entropy_context *ctx );
     mbedtls_entropy_context entropy;
     mbedtls_ctr_drbg_context ctr_drbg;
     key_slot_t key_slots[PSA_KEY_SLOT_COUNT];
@@ -4437,6 +4440,17 @@ psa_status_t psa_generate_key( psa_key_slot_t key,
 /* Module setup */
 /****************************************************************/
 
+psa_status_t mbedtls_psa_crypto_configure_entropy_sources(
+    void (* entropy_init )( mbedtls_entropy_context *ctx ),
+    void (* entropy_free )( mbedtls_entropy_context *ctx ) )
+{
+    if( global_data.rng_state != RNG_NOT_INITIALIZED )
+        return( PSA_ERROR_BAD_STATE );
+    global_data.entropy_init = entropy_init;
+    global_data.entropy_free = entropy_free;
+    return( PSA_SUCCESS );
+}
+
 void mbedtls_psa_crypto_free( void )
 {
     psa_key_slot_t key;
@@ -4457,7 +4471,7 @@ void mbedtls_psa_crypto_free( void )
     if( global_data.rng_state != RNG_NOT_INITIALIZED )
     {
         mbedtls_ctr_drbg_free( &global_data.ctr_drbg );
-        mbedtls_entropy_free( &global_data.entropy );
+        global_data.entropy_free( &global_data.entropy );
     }
     /* Wipe all remaining data, including configuration.
      * In particular, this sets all state indicator to the value
@@ -4474,10 +4488,15 @@ psa_status_t psa_crypto_init( void )
     if( global_data.initialized != 0 )
         return( PSA_SUCCESS );
 
-    mbedtls_zeroize( &global_data, sizeof( global_data ) );
+    /* Set default configuration if
+     * mbedtls_psa_crypto_configure_entropy_sources() hasn't been called. */
+    if( global_data.entropy_init == NULL )
+        global_data.entropy_init = mbedtls_entropy_init;
+    if( global_data.entropy_free == NULL )
+        global_data.entropy_free = mbedtls_entropy_free;
 
     /* Initialize the random generator. */
-    mbedtls_entropy_init( &global_data.entropy );
+    global_data.entropy_init( &global_data.entropy );
     mbedtls_ctr_drbg_init( &global_data.ctr_drbg );
     global_data.rng_state = RNG_INITIALIZED;
     ret = mbedtls_ctr_drbg_seed( &global_data.ctr_drbg,

library/psa_crypto_invasive.h

@@ -0,0 +1,79 @@
+/**
+ * \file psa_crypto_invasive.h
+ *
+ * \brief PSA cryptography module: invasive interfaces for test only.
+ *
+ * The interfaces in this file are intended for testing purposes only.
+ * They MUST NOT be made available to clients over IPC in integrations
+ * with isolation, and they SHOULD NOT be made available in library
+ * integrations except when building the library for testing.
+ */
+/*
+ *  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 PSA_CRYPTO_INVASIVE_H
+#define PSA_CRYPTO_INVASIVE_H
+
+#if defined(MBEDTLS_CONFIG_FILE)
+#include MBEDTLS_CONFIG_FILE
+#else
+#include "mbedtls/config.h"
+#endif
+
+#include "psa/crypto.h"
+
+#include "mbedtls/entropy.h"
+
+/** \brief Configure entropy sources.
+ *
+ * This function may only be called before a call to psa_crypto_init(),
+ * or after a call to mbedtls_psa_crypto_free() and before any
+ * subsequent call to psa_crypto_init().
+ *
+ * This function is only intended for test purposes. The functionality
+ * it provides is also useful for system integrators, but
+ * system integrators should configure entropy drivers instead of
+ * breaking through to the Mbed TLS API.
+ *
+ * \param entropy_init  Function to initialize the entropy context
+ *                      and set up the desired entropy sources.
+ *                      It is called by psa_crypto_init().
+ *                      By default this is mbedtls_entropy_init().
+ *                      This function cannot report failures directly.
+ *                      To indicate a failure, set the entropy context
+ *                      to a state where mbedtls_entropy_func() will
+ *                      return an error.
+ * \param entropy_free  Function to free the entropy context
+ *                      and associated resources.
+ *                      It is called by mbedtls_psa_crypto_free().
+ *                      By default this is mbedtls_entropy_free().
+ *
+ * \retval PSA_SUCCESS
+ *         Success.
+ * \retval PSA_ERROR_NOT_PERMITTED
+ *         The caller does not have the permission to configure
+ *         entropy sources.
+ * \retval PSA_ERROR_BAD_STATE
+ *         The library has already been initialized.
+ */
+psa_status_t mbedtls_psa_crypto_configure_entropy_sources(
+    void (* entropy_init )( mbedtls_entropy_context *ctx ),
+    void (* entropy_free )( mbedtls_entropy_context *ctx ) );
+
+#endif /* PSA_CRYPTO_INVASIVE_H */

tests/suites/test_suite_psa_crypto_init.data

@@ -18,3 +18,9 @@ validate_module_init_generate_random:1
 
 No key slot access after deinit
 validate_module_init_key_based:1
+
+Custom entropy sources: all standard
+custom_entropy_sources:0x0000ffff:PSA_SUCCESS
+
+Custom entropy sources: none
+custom_entropy_sources:0:PSA_ERROR_INSUFFICIENT_ENTROPY

tests/suites/test_suite_psa_crypto_init.function

@@ -6,6 +6,73 @@
 #endif
 #include "psa/crypto.h"
 
+/* Some tests in this module configure entropy sources. */
+#include "psa_crypto_invasive.h"
+
+#include "mbedtls/entropy.h"
+#include "mbedtls/entropy_poll.h"
+
+#define ENTROPY_SOURCE_PLATFORM                 0x00000001
+#define ENTROPY_SOURCE_TIMING                   0x00000002
+#define ENTROPY_SOURCE_HAVEGE                   0x00000004
+#define ENTROPY_SOURCE_HARDWARE                 0x00000008
+#define ENTROPY_SOURCE_NV_SEED                  0x00000010
+static uint32_t custom_entropy_sources_mask;
+
+/* This is a modified version of mbedtls_entropy_init() from entropy.c
+ * which chooses entropy sources dynamically. */
+static void custom_entropy_init( mbedtls_entropy_context *ctx )
+{
+    ctx->source_count = 0;
+    memset( ctx->source, 0, sizeof( ctx->source ) );
+
+#if defined(MBEDTLS_THREADING_C)
+    mbedtls_mutex_init( &ctx->mutex );
+#endif
+
+    ctx->accumulator_started = 0;
+#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
+    mbedtls_sha512_init( &ctx->accumulator );
+#else
+    mbedtls_sha256_init( &ctx->accumulator );
+#endif
+#if defined(MBEDTLS_HAVEGE_C)
+    mbedtls_havege_init( &ctx->havege_data );
+#endif
+
+#if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
+    if( custom_entropy_sources_mask & ENTROPY_SOURCE_PLATFORM )
+        mbedtls_entropy_add_source( ctx, mbedtls_platform_entropy_poll, NULL,
+                                    MBEDTLS_ENTROPY_MIN_PLATFORM,
+                                    MBEDTLS_ENTROPY_SOURCE_STRONG );
+#endif
+#if defined(MBEDTLS_TIMING_C)
+    if( custom_entropy_sources_mask & ENTROPY_SOURCE_TIMING )
+        mbedtls_entropy_add_source( ctx, mbedtls_hardclock_poll, NULL,
+                                    MBEDTLS_ENTROPY_MIN_HARDCLOCK,
+                                    MBEDTLS_ENTROPY_SOURCE_WEAK );
+#endif
+#if defined(MBEDTLS_HAVEGE_C)
+    if( custom_entropy_sources_mask & ENTROPY_SOURCE_HAVEGE )
+        mbedtls_entropy_add_source( ctx, mbedtls_havege_poll, &ctx->havege_data,
+                                    MBEDTLS_ENTROPY_MIN_HAVEGE,
+                                    MBEDTLS_ENTROPY_SOURCE_STRONG );
+#endif
+#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
+    if( custom_entropy_sources_mask & ENTROPY_SOURCE_HARDWARE )
+        mbedtls_entropy_add_source( ctx, mbedtls_hardware_poll, NULL,
+                                    MBEDTLS_ENTROPY_MIN_HARDWARE,
+                                    MBEDTLS_ENTROPY_SOURCE_STRONG );
+#endif
+#if defined(MBEDTLS_ENTROPY_NV_SEED)
+    if( custom_entropy_sources_mask & ENTROPY_SOURCE_NV_SEED )
+        mbedtls_entropy_add_source( ctx, mbedtls_nv_seed_poll, NULL,
+                                    MBEDTLS_ENTROPY_BLOCK_SIZE,
+                                    MBEDTLS_ENTROPY_SOURCE_STRONG );
+    ctx->initial_entropy_run = 0;
+#endif
+}
+
 /* END_HEADER */
 
 /* BEGIN_DEPENDENCIES
@@ -75,3 +142,29 @@ void validate_module_init_key_based( int count )
     TEST_ASSERT( status == PSA_ERROR_BAD_STATE );
 }
 /* END_CASE */
+
+/* BEGIN_CASE */
+void custom_entropy_sources( int sources_arg, int expected_init_status_arg )
+{
+    psa_status_t expected_init_status = expected_init_status_arg;
+    int inited = 0;
+    uint8_t random[10] = { 0 };
+
+    custom_entropy_sources_mask = sources_arg;
+    TEST_ASSERT( mbedtls_psa_crypto_configure_entropy_sources(
+                     custom_entropy_init, mbedtls_entropy_free ) ==
+                 PSA_SUCCESS );
+
+    TEST_ASSERT( psa_crypto_init( ) == expected_init_status );
+    if( expected_init_status != PSA_SUCCESS )
+        goto exit;
+    inited = 1;
+
+    TEST_ASSERT( psa_generate_random( random, sizeof( random ) ) ==
+                 PSA_SUCCESS );
+
+exit:
+    if( inited )
+        mbedtls_psa_crypto_free( );
+}
+/* END_CASE */