From 65fc0686a7df290fc3f0f58d318241bf8f61c76a Mon Sep 17 00:00:00 2001
From: Gilles Peskine <Gilles.Peskine@arm.com>
Date: Tue, 8 Oct 2019 15:01:34 +0200
Subject: [PATCH] Add tests to ensure that we gather as much entropy as
 expected

There were tests to ensure that each entropy source reaches its
threshold, but no test that covers the total amount of entropy. Add
test cases with a known set of entropy sources and make sure that we
always gather at least MBEDTLS_ENTROPY_BLOCK_SIZE bytes from a strong
source.
---
 tests/suites/test_suite_entropy.data     | 18 ++++++++++
 tests/suites/test_suite_entropy.function | 43 ++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/tests/suites/test_suite_entropy.data b/tests/suites/test_suite_entropy.data
index abf36c0ec..b2d20b472 100644
--- a/tests/suites/test_suite_entropy.data
+++ b/tests/suites/test_suite_entropy.data
@@ -43,6 +43,24 @@ entropy_threshold:16:0:MBEDTLS_ERR_ENTROPY_SOURCE_FAILED
 Entropy threshold: 1024 never reached
 entropy_threshold:1024:1:MBEDTLS_ERR_ENTROPY_SOURCE_FAILED
 
+Entropy calls: no strong
+entropy_calls:MBEDTLS_ENTROPY_SOURCE_WEAK:MBEDTLS_ENTROPY_SOURCE_WEAK:1:MBEDTLS_ENTROPY_BLOCK_SIZE:MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE
+
+Entropy calls: 1 strong, 1*BLOCK_SIZE
+entropy_calls:MBEDTLS_ENTROPY_SOURCE_STRONG:MBEDTLS_ENTROPY_SOURCE_WEAK:1:MBEDTLS_ENTROPY_BLOCK_SIZE:1
+
+Entropy calls: 1 strong, 2*(BLOCK_SIZE/2)
+entropy_calls:MBEDTLS_ENTROPY_SOURCE_STRONG:MBEDTLS_ENTROPY_SOURCE_WEAK:1:(MBEDTLS_ENTROPY_BLOCK_SIZE+1)/2:2
+
+Entropy calls: 1 strong, BLOCK_SIZE*1
+entropy_calls:MBEDTLS_ENTROPY_SOURCE_STRONG:MBEDTLS_ENTROPY_SOURCE_WEAK:1:1:MBEDTLS_ENTROPY_BLOCK_SIZE
+
+Entropy calls: 1 strong, 2*BLOCK_SIZE to reach threshold
+entropy_calls:MBEDTLS_ENTROPY_SOURCE_STRONG:MBEDTLS_ENTROPY_SOURCE_WEAK:MBEDTLS_ENTROPY_BLOCK_SIZE+1:MBEDTLS_ENTROPY_BLOCK_SIZE:2
+
+Entropy calls: 2 strong, BLOCK_SIZE/2 each
+entropy_calls:MBEDTLS_ENTROPY_SOURCE_STRONG:MBEDTLS_ENTROPY_SOURCE_WEAK:(MBEDTLS_ENTROPY_BLOCK_SIZE+1)/2:(MBEDTLS_ENTROPY_BLOCK_SIZE+1)/2:2
+
 Check NV seed standard IO
 entropy_nv_seed_std_io:
 
diff --git a/tests/suites/test_suite_entropy.function b/tests/suites/test_suite_entropy.function
index a125f6202..d1d88c5fa 100644
--- a/tests/suites/test_suite_entropy.function
+++ b/tests/suites/test_suite_entropy.function
@@ -286,6 +286,49 @@ exit:
 }
 /* END_CASE */
 
+/* BEGIN_CASE */
+void entropy_calls( int strength1, int strength2,
+                    int threshold, int chunk_size,
+                    int result )
+{
+    /*
+     * if result >= 0: result = expected number of calls to source 1
+     * if result < 0: result = expected return code from mbedtls_entropy_func()
+     */
+
+    mbedtls_entropy_context ctx;
+    entropy_dummy_context dummy1 = {DUMMY_CONSTANT_LENGTH, chunk_size, 0};
+    entropy_dummy_context dummy2 = {DUMMY_CONSTANT_LENGTH, chunk_size, 0};
+    unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
+    int ret;
+
+    mbedtls_entropy_init( &ctx );
+    entropy_clear_sources( &ctx );
+
+    TEST_ASSERT( mbedtls_entropy_add_source( &ctx, entropy_dummy_source,
+                                             &dummy1, threshold,
+                                             strength1 ) == 0 );
+    TEST_ASSERT( mbedtls_entropy_add_source( &ctx, entropy_dummy_source,
+                                             &dummy2, threshold,
+                                             strength2 ) == 0 );
+
+    ret = mbedtls_entropy_func( &ctx, buf, sizeof( buf ) );
+
+    if( result >= 0 )
+    {
+        TEST_ASSERT( ret == 0 );
+        TEST_ASSERT( dummy1.calls == (size_t) result );
+    }
+    else
+    {
+        TEST_ASSERT( ret == result );
+    }
+
+exit:
+    mbedtls_entropy_free( &ctx );
+}
+/* END_CASE */
+
 /* BEGIN_CASE depends_on:MBEDTLS_ENTROPY_NV_SEED:MBEDTLS_FS_IO */
 void nv_seed_file_create(  )
 {