Flatten Mbed TLS directory structure

third_party/mbedtls/entropy.c

@@ -0,0 +1,735 @@
+/* clang-format off */
+
+asm(".ident\t\"\\n\\n\
+Mbed TLS (Apache 2.0)\\n\
+Copyright The Mbed TLS Contributors\"");
+asm(".include \"libc/disclaimer.inc\"");
+
+/*
+ *  Entropy accumulator implementation
+ *
+ *  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.
+ */
+
+#include "libc/calls/calls.h"
+#include "libc/stdio/stdio.h"
+#include "third_party/mbedtls/common.h"
+
+#if defined(MBEDTLS_ENTROPY_C)
+
+#if defined(MBEDTLS_TEST_NULL_ENTROPY)
+#warning "**** WARNING!  MBEDTLS_TEST_NULL_ENTROPY defined! "
+#warning "**** THIS BUILD HAS NO DEFINED ENTROPY SOURCES "
+#warning "**** THIS BUILD IS *NOT* SUITABLE FOR PRODUCTION USE "
+#endif
+
+#include "third_party/mbedtls/entropy.h"
+#include "third_party/mbedtls/entropy_poll.h"
+#include "third_party/mbedtls/platform_util.h"
+#include "third_party/mbedtls/error.h"
+
+
+#if defined(MBEDTLS_FS_IO)
+#endif
+
+#if defined(MBEDTLS_ENTROPY_NV_SEED)
+#include "third_party/mbedtls/platform.h"
+#endif
+
+#if defined(MBEDTLS_SELF_TEST)
+#if defined(MBEDTLS_PLATFORM_C)
+#include "third_party/mbedtls/platform.h"
+#else
+#define mbedtls_printf     printf
+#endif /* MBEDTLS_PLATFORM_C */
+#endif /* MBEDTLS_SELF_TEST */
+
+#if defined(MBEDTLS_HAVEGE_C)
+#include "third_party/mbedtls/havege.h"
+#endif
+
+#define ENTROPY_MAX_LOOP    256     /**< Maximum amount to loop before error */
+
+void mbedtls_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
+
+    /* Reminder: Update ENTROPY_HAVE_STRONG in the test files
+     *           when adding more strong entropy sources here. */
+
+#if defined(MBEDTLS_TEST_NULL_ENTROPY)
+    mbedtls_entropy_add_source( ctx, mbedtls_null_entropy_poll, NULL,
+                                1, MBEDTLS_ENTROPY_SOURCE_STRONG );
+#endif
+
+#if !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES)
+#if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
+    mbedtls_entropy_add_source( ctx, mbedtls_platform_entropy_poll, NULL,
+                                MBEDTLS_ENTROPY_MIN_PLATFORM,
+                                MBEDTLS_ENTROPY_SOURCE_STRONG );
+#endif
+#if defined(MBEDTLS_TIMING_C)
+    mbedtls_entropy_add_source( ctx, mbedtls_hardclock_poll, NULL,
+                                MBEDTLS_ENTROPY_MIN_HARDCLOCK,
+                                MBEDTLS_ENTROPY_SOURCE_WEAK );
+#endif
+#if defined(MBEDTLS_HAVEGE_C)
+    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)
+    mbedtls_entropy_add_source( ctx, mbedtls_hardware_poll, NULL,
+                                MBEDTLS_ENTROPY_MIN_HARDWARE,
+                                MBEDTLS_ENTROPY_SOURCE_STRONG );
+#endif
+#if defined(MBEDTLS_ENTROPY_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
+#endif /* MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES */
+}
+
+void mbedtls_entropy_free( mbedtls_entropy_context *ctx )
+{
+    /* If the context was already free, don't call free() again.
+     * This is important for mutexes which don't allow double-free. */
+    if( ctx->accumulator_started == -1 )
+        return;
+
+#if defined(MBEDTLS_HAVEGE_C)
+    mbedtls_havege_free( &ctx->havege_data );
+#endif
+#if defined(MBEDTLS_THREADING_C)
+    mbedtls_mutex_free( &ctx->mutex );
+#endif
+#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
+    mbedtls_sha512_free( &ctx->accumulator );
+#else
+    mbedtls_sha256_free( &ctx->accumulator );
+#endif
+#if defined(MBEDTLS_ENTROPY_NV_SEED)
+    ctx->initial_entropy_run = 0;
+#endif
+    ctx->source_count = 0;
+    mbedtls_platform_zeroize( ctx->source, sizeof( ctx->source ) );
+    ctx->accumulator_started = -1;
+}
+
+int mbedtls_entropy_add_source( mbedtls_entropy_context *ctx,
+                        mbedtls_entropy_f_source_ptr f_source, void *p_source,
+                        size_t threshold, int strong )
+{
+    int idx, ret = 0;
+
+#if defined(MBEDTLS_THREADING_C)
+    if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
+        return( ret );
+#endif
+
+    idx = ctx->source_count;
+    if( idx >= MBEDTLS_ENTROPY_MAX_SOURCES )
+    {
+        ret = MBEDTLS_ERR_ENTROPY_MAX_SOURCES;
+        goto exit;
+    }
+
+    ctx->source[idx].f_source  = f_source;
+    ctx->source[idx].p_source  = p_source;
+    ctx->source[idx].threshold = threshold;
+    ctx->source[idx].strong    = strong;
+
+    ctx->source_count++;
+
+exit:
+#if defined(MBEDTLS_THREADING_C)
+    if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
+        return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+#endif
+
+    return( ret );
+}
+
+/*
+ * Entropy accumulator update
+ */
+static int entropy_update( mbedtls_entropy_context *ctx, unsigned char source_id,
+                           const unsigned char *data, size_t len )
+{
+    unsigned char header[2];
+    unsigned char tmp[MBEDTLS_ENTROPY_BLOCK_SIZE];
+    size_t use_len = len;
+    const unsigned char *p = data;
+    int ret = 0;
+
+    if( use_len > MBEDTLS_ENTROPY_BLOCK_SIZE )
+    {
+#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
+        if( ( ret = mbedtls_sha512_ret( data, len, tmp, 0 ) ) != 0 )
+            goto cleanup;
+#else
+        if( ( ret = mbedtls_sha256_ret( data, len, tmp, 0 ) ) != 0 )
+            goto cleanup;
+#endif
+        p = tmp;
+        use_len = MBEDTLS_ENTROPY_BLOCK_SIZE;
+    }
+
+    header[0] = source_id;
+    header[1] = use_len & 0xFF;
+
+    /*
+     * Start the accumulator if this has not already happened. Note that
+     * it is sufficient to start the accumulator here only because all calls to
+     * gather entropy eventually execute this code.
+     */
+#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
+    if( ctx->accumulator_started == 0 &&
+        ( ret = mbedtls_sha512_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
+        goto cleanup;
+    else
+        ctx->accumulator_started = 1;
+    if( ( ret = mbedtls_sha512_update_ret( &ctx->accumulator, header, 2 ) ) != 0 )
+        goto cleanup;
+    ret = mbedtls_sha512_update_ret( &ctx->accumulator, p, use_len );
+#else
+    if( ctx->accumulator_started == 0 &&
+        ( ret = mbedtls_sha256_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
+        goto cleanup;
+    else
+        ctx->accumulator_started = 1;
+    if( ( ret = mbedtls_sha256_update_ret( &ctx->accumulator, header, 2 ) ) != 0 )
+        goto cleanup;
+    ret = mbedtls_sha256_update_ret( &ctx->accumulator, p, use_len );
+#endif
+
+cleanup:
+    mbedtls_platform_zeroize( tmp, sizeof( tmp ) );
+
+    return( ret );
+}
+
+int mbedtls_entropy_update_manual( mbedtls_entropy_context *ctx,
+                           const unsigned char *data, size_t len )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+#if defined(MBEDTLS_THREADING_C)
+    if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
+        return( ret );
+#endif
+
+    ret = entropy_update( ctx, MBEDTLS_ENTROPY_SOURCE_MANUAL, data, len );
+
+#if defined(MBEDTLS_THREADING_C)
+    if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
+        return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+#endif
+
+    return( ret );
+}
+
+/*
+ * Run through the different sources to add entropy to our accumulator
+ */
+static int entropy_gather_internal( mbedtls_entropy_context *ctx )
+{
+    int ret = MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
+    int i;
+    int have_one_strong = 0;
+    unsigned char buf[MBEDTLS_ENTROPY_MAX_GATHER];
+    size_t olen;
+
+    if( ctx->source_count == 0 )
+        return( MBEDTLS_ERR_ENTROPY_NO_SOURCES_DEFINED );
+
+    /*
+     * Run through our entropy sources
+     */
+    for( i = 0; i < ctx->source_count; i++ )
+    {
+        if( ctx->source[i].strong == MBEDTLS_ENTROPY_SOURCE_STRONG )
+            have_one_strong = 1;
+
+        olen = 0;
+        if( ( ret = ctx->source[i].f_source( ctx->source[i].p_source,
+                        buf, MBEDTLS_ENTROPY_MAX_GATHER, &olen ) ) != 0 )
+        {
+            goto cleanup;
+        }
+
+        /*
+         * Add if we actually gathered something
+         */
+        if( olen > 0 )
+        {
+            if( ( ret = entropy_update( ctx, (unsigned char) i,
+                                        buf, olen ) ) != 0 )
+                return( ret );
+            ctx->source[i].size += olen;
+        }
+    }
+
+    if( have_one_strong == 0 )
+        ret = MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE;
+
+cleanup:
+    mbedtls_platform_zeroize( buf, sizeof( buf ) );
+
+    return( ret );
+}
+
+/*
+ * Thread-safe wrapper for entropy_gather_internal()
+ */
+int mbedtls_entropy_gather( mbedtls_entropy_context *ctx )
+{
+    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+
+#if defined(MBEDTLS_THREADING_C)
+    if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
+        return( ret );
+#endif
+
+    ret = entropy_gather_internal( ctx );
+
+#if defined(MBEDTLS_THREADING_C)
+    if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
+        return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+#endif
+
+    return( ret );
+}
+
+int mbedtls_entropy_func( void *data, unsigned char *output, size_t len )
+{
+    int ret, count = 0, i, thresholds_reached;
+    size_t strong_size;
+    mbedtls_entropy_context *ctx = (mbedtls_entropy_context *) data;
+    unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];
+
+    if( len > MBEDTLS_ENTROPY_BLOCK_SIZE )
+        return( MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );
+
+#if defined(MBEDTLS_ENTROPY_NV_SEED)
+    /* Update the NV entropy seed before generating any entropy for outside
+     * use.
+     */
+    if( ctx->initial_entropy_run == 0 )
+    {
+        ctx->initial_entropy_run = 1;
+        if( ( ret = mbedtls_entropy_update_nv_seed( ctx ) ) != 0 )
+            return( ret );
+    }
+#endif
+
+#if defined(MBEDTLS_THREADING_C)
+    if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
+        return( ret );
+#endif
+
+    /*
+     * Always gather extra entropy before a call
+     */
+    do
+    {
+        if( count++ > ENTROPY_MAX_LOOP )
+        {
+            ret = MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
+            goto exit;
+        }
+
+        if( ( ret = entropy_gather_internal( ctx ) ) != 0 )
+            goto exit;
+
+        thresholds_reached = 1;
+        strong_size = 0;
+        for( i = 0; i < ctx->source_count; i++ )
+        {
+            if( ctx->source[i].size < ctx->source[i].threshold )
+                thresholds_reached = 0;
+            if( ctx->source[i].strong == MBEDTLS_ENTROPY_SOURCE_STRONG )
+                strong_size += ctx->source[i].size;
+        }
+    }
+    while( ! thresholds_reached || strong_size < MBEDTLS_ENTROPY_BLOCK_SIZE );
+
+    memset( buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE );
+
+#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
+    /*
+     * Note that at this stage it is assumed that the accumulator was started
+     * in a previous call to entropy_update(). If this is not guaranteed, the
+     * code below will fail.
+     */
+    if( ( ret = mbedtls_sha512_finish_ret( &ctx->accumulator, buf ) ) != 0 )
+        goto exit;
+
+    /*
+     * Reset accumulator and counters and recycle existing entropy
+     */
+    mbedtls_sha512_free( &ctx->accumulator );
+    mbedtls_sha512_init( &ctx->accumulator );
+    if( ( ret = mbedtls_sha512_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
+        goto exit;
+    if( ( ret = mbedtls_sha512_update_ret( &ctx->accumulator, buf,
+                                           MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
+        goto exit;
+
+    /*
+     * Perform second SHA-512 on entropy
+     */
+    if( ( ret = mbedtls_sha512_ret( buf, MBEDTLS_ENTROPY_BLOCK_SIZE,
+                                    buf, 0 ) ) != 0 )
+        goto exit;
+#else /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */
+    if( ( ret = mbedtls_sha256_finish_ret( &ctx->accumulator, buf ) ) != 0 )
+        goto exit;
+
+    /*
+     * Reset accumulator and counters and recycle existing entropy
+     */
+    mbedtls_sha256_free( &ctx->accumulator );
+    mbedtls_sha256_init( &ctx->accumulator );
+    if( ( ret = mbedtls_sha256_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
+        goto exit;
+    if( ( ret = mbedtls_sha256_update_ret( &ctx->accumulator, buf,
+                                           MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
+        goto exit;
+
+    /*
+     * Perform second SHA-256 on entropy
+     */
+    if( ( ret = mbedtls_sha256_ret( buf, MBEDTLS_ENTROPY_BLOCK_SIZE,
+                                    buf, 0 ) ) != 0 )
+        goto exit;
+#endif /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */
+
+    for( i = 0; i < ctx->source_count; i++ )
+        ctx->source[i].size = 0;
+
+    memcpy( output, buf, len );
+
+    ret = 0;
+
+exit:
+    mbedtls_platform_zeroize( buf, sizeof( buf ) );
+
+#if defined(MBEDTLS_THREADING_C)
+    if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
+        return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
+#endif
+
+    return( ret );
+}
+
+#if defined(MBEDTLS_ENTROPY_NV_SEED)
+int mbedtls_entropy_update_nv_seed( mbedtls_entropy_context *ctx )
+{
+    int ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
+    unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];
+
+    /* Read new seed  and write it to NV */
+    if( ( ret = mbedtls_entropy_func( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
+        return( ret );
+
+    if( mbedtls_nv_seed_write( buf, MBEDTLS_ENTROPY_BLOCK_SIZE ) < 0 )
+        return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );
+
+    /* Manually update the remaining stream with a separator value to diverge */
+    memset( buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE );
+    ret = mbedtls_entropy_update_manual( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE );
+
+    return( ret );
+}
+#endif /* MBEDTLS_ENTROPY_NV_SEED */
+
+#if defined(MBEDTLS_FS_IO)
+int mbedtls_entropy_write_seed_file( mbedtls_entropy_context *ctx, const char *path )
+{
+    int ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
+    FILE *f;
+    unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];
+
+    if( ( f = fopen( path, "wb" ) ) == NULL )
+        return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );
+
+    if( ( ret = mbedtls_entropy_func( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
+        goto exit;
+
+    if( fwrite( buf, 1, MBEDTLS_ENTROPY_BLOCK_SIZE, f ) != MBEDTLS_ENTROPY_BLOCK_SIZE )
+    {
+        ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
+        goto exit;
+    }
+
+    ret = 0;
+
+exit:
+    mbedtls_platform_zeroize( buf, sizeof( buf ) );
+
+    fclose( f );
+    return( ret );
+}
+
+int mbedtls_entropy_update_seed_file( mbedtls_entropy_context *ctx, const char *path )
+{
+    int ret = 0;
+    FILE *f;
+    size_t n;
+    unsigned char buf[ MBEDTLS_ENTROPY_MAX_SEED_SIZE ];
+
+    if( ( f = fopen( path, "rb" ) ) == NULL )
+        return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );
+
+    fseek( f, 0, SEEK_END );
+    n = (size_t) ftell( f );
+    fseek( f, 0, SEEK_SET );
+
+    if( n > MBEDTLS_ENTROPY_MAX_SEED_SIZE )
+        n = MBEDTLS_ENTROPY_MAX_SEED_SIZE;
+
+    if( fread( buf, 1, n, f ) != n )
+        ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
+    else
+        ret = mbedtls_entropy_update_manual( ctx, buf, n );
+
+    fclose( f );
+
+    mbedtls_platform_zeroize( buf, sizeof( buf ) );
+
+    if( ret != 0 )
+        return( ret );
+
+    return( mbedtls_entropy_write_seed_file( ctx, path ) );
+}
+#endif /* MBEDTLS_FS_IO */
+
+#if defined(MBEDTLS_SELF_TEST)
+#if !defined(MBEDTLS_TEST_NULL_ENTROPY)
+/*
+ * Dummy source function
+ */
+static int entropy_dummy_source( void *data, unsigned char *output,
+                                 size_t len, size_t *olen )
+{
+    ((void) data);
+
+    memset( output, 0x2a, len );
+    *olen = len;
+
+    return( 0 );
+}
+#endif /* !MBEDTLS_TEST_NULL_ENTROPY */
+
+#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
+
+static int mbedtls_entropy_source_self_test_gather( unsigned char *buf, size_t buf_len )
+{
+    int ret = 0;
+    size_t entropy_len = 0;
+    size_t olen = 0;
+    size_t attempts = buf_len;
+
+    while( attempts > 0 && entropy_len < buf_len )
+    {
+        if( ( ret = mbedtls_hardware_poll( NULL, buf + entropy_len,
+            buf_len - entropy_len, &olen ) ) != 0 )
+            return( ret );
+
+        entropy_len += olen;
+        attempts--;
+    }
+
+    if( entropy_len < buf_len )
+    {
+        ret = 1;
+    }
+
+    return( ret );
+}
+
+
+static int mbedtls_entropy_source_self_test_check_bits( const unsigned char *buf,
+                                                        size_t buf_len )
+{
+    unsigned char set= 0xFF;
+    unsigned char unset = 0x00;
+    size_t i;
+
+    for( i = 0; i < buf_len; i++ )
+    {
+        set &= buf[i];
+        unset |= buf[i];
+    }
+
+    return( set == 0xFF || unset == 0x00 );
+}
+
+/*
+ * A test to ensure hat the entropy sources are functioning correctly
+ * and there is no obvious failure. The test performs the following checks:
+ *  - The entropy source is not providing only 0s (all bits unset) or 1s (all
+ *    bits set).
+ *  - The entropy source is not providing values in a pattern. Because the
+ *    hardware could be providing data in an arbitrary length, this check polls
+ *    the hardware entropy source twice and compares the result to ensure they
+ *    are not equal.
+ *  - The error code returned by the entropy source is not an error.
+ */
+int mbedtls_entropy_source_self_test( int verbose )
+{
+    int ret = 0;
+    unsigned char buf0[2 * sizeof( unsigned long long int )];
+    unsigned char buf1[2 * sizeof( unsigned long long int )];
+
+    if( verbose != 0 )
+        mbedtls_printf( "  ENTROPY_BIAS test: " );
+
+    memset( buf0, 0x00, sizeof( buf0 ) );
+    memset( buf1, 0x00, sizeof( buf1 ) );
+
+    if( ( ret = mbedtls_entropy_source_self_test_gather( buf0, sizeof( buf0 ) ) ) != 0 )
+        goto cleanup;
+    if( ( ret = mbedtls_entropy_source_self_test_gather( buf1, sizeof( buf1 ) ) ) != 0 )
+        goto cleanup;
+
+    /* Make sure that the returned values are not all 0 or 1 */
+    if( ( ret = mbedtls_entropy_source_self_test_check_bits( buf0, sizeof( buf0 ) ) ) != 0 )
+        goto cleanup;
+    if( ( ret = mbedtls_entropy_source_self_test_check_bits( buf1, sizeof( buf1 ) ) ) != 0 )
+        goto cleanup;
+
+    /* Make sure that the entropy source is not returning values in a
+     * pattern */
+    ret = memcmp( buf0, buf1, sizeof( buf0 ) ) == 0;
+
+cleanup:
+    if( verbose != 0 )
+    {
+        if( ret != 0 )
+            mbedtls_printf( "failed\n" );
+        else
+            mbedtls_printf( "passed\n" );
+
+        mbedtls_printf( "\n" );
+    }
+
+    return( ret != 0 );
+}
+
+#endif /* MBEDTLS_ENTROPY_HARDWARE_ALT */
+
+/*
+ * The actual entropy quality is hard to test, but we can at least
+ * test that the functions don't cause errors and write the correct
+ * amount of data to buffers.
+ */
+int mbedtls_entropy_self_test( int verbose )
+{
+    int ret = 1;
+#if !defined(MBEDTLS_TEST_NULL_ENTROPY)
+    mbedtls_entropy_context ctx;
+    unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
+    unsigned char acc[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
+    size_t i, j;
+#endif /* !MBEDTLS_TEST_NULL_ENTROPY */
+
+    if( verbose != 0 )
+        mbedtls_printf( "  ENTROPY test: " );
+
+#if !defined(MBEDTLS_TEST_NULL_ENTROPY)
+    mbedtls_entropy_init( &ctx );
+
+    /* First do a gather to make sure we have default sources */
+    if( ( ret = mbedtls_entropy_gather( &ctx ) ) != 0 )
+        goto cleanup;
+
+    ret = mbedtls_entropy_add_source( &ctx, entropy_dummy_source, NULL, 16,
+                                      MBEDTLS_ENTROPY_SOURCE_WEAK );
+    if( ret != 0 )
+        goto cleanup;
+
+    if( ( ret = mbedtls_entropy_update_manual( &ctx, buf, sizeof buf ) ) != 0 )
+        goto cleanup;
+
+    /*
+     * To test that mbedtls_entropy_func writes correct number of bytes:
+     * - use the whole buffer and rely on ASan to detect overruns
+     * - collect entropy 8 times and OR the result in an accumulator:
+     *   any byte should then be 0 with probably 2^(-64), so requiring
+     *   each of the 32 or 64 bytes to be non-zero has a false failure rate
+     *   of at most 2^(-58) which is acceptable.
+     */
+    for( i = 0; i < 8; i++ )
+    {
+        if( ( ret = mbedtls_entropy_func( &ctx, buf, sizeof( buf ) ) ) != 0 )
+            goto cleanup;
+
+        for( j = 0; j < sizeof( buf ); j++ )
+            acc[j] |= buf[j];
+    }
+
+    for( j = 0; j < sizeof( buf ); j++ )
+    {
+        if( acc[j] == 0 )
+        {
+            ret = 1;
+            goto cleanup;
+        }
+    }
+
+#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
+    if( ( ret = mbedtls_entropy_source_self_test( 0 ) ) != 0 )
+        goto cleanup;
+#endif
+
+cleanup:
+    mbedtls_entropy_free( &ctx );
+#endif /* !MBEDTLS_TEST_NULL_ENTROPY */
+
+    if( verbose != 0 )
+    {
+        if( ret != 0 )
+            mbedtls_printf( "failed\n" );
+        else
+            mbedtls_printf( "passed\n" );
+
+        mbedtls_printf( "\n" );
+    }
+
+    return( ret != 0 );
+}
+#endif /* MBEDTLS_SELF_TEST */
+
+#endif /* MBEDTLS_ENTROPY_C */