[rng] Allow for entropy sources that fail during startup tests

Provide per-source state variables for the repetition count test and
adaptive proportion test, to allow for the situation in which an
entropy source can be enabled but then fails during the startup tests,
thereby requiring an alternative entropy source to be used.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 227 insertions, 122 deletions

diff --git a/src/crypto/entropy.c b/src/crypto/entropy.c
index 204e6bb1e..419007159 100644
--- a/src/crypto/entropy.c
+++ b/src/crypto/entropy.c
@@ -50,77 +50,34 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define EINFO_EPIPE_ADAPTIVE_PROPORTION_TEST \
 	__einfo_uniqify ( EINFO_EPIPE, 0x02, "Adaptive proportion test failed" )
 
-/** Current entropy source */
-static struct entropy_source *entropy_source;
-
 /**
- * Enable entropy gathering
+ * Initialise repetition count test
  *
- * @ret rc		Return status code
+ * @v source		Entropy source
  */
-int entropy_enable ( void ) {
-	int rc;
-
-	/* Enable selected source, if applicable */
-	if ( entropy_source ) {
-
-		/* Enable entropy source */
-		if ( ( rc = entropy_source->enable() ) != 0 ) {
-			DBGC ( &entropy_source, "ENTROPY could not enable "
-			       "source \"%s\": %s\n", entropy_source->name,
-			       strerror ( rc ) );
-			return rc;
-		}
-
-		/* Sanity checks */
-		assert ( entropy_source->min_entropy_per_sample > 0 );
-		assert ( entropy_source->repetition_count_cutoff > 0 );
-		assert ( entropy_source->adaptive_proportion_cutoff > 0 );
-		assert ( entropy_source->startup_test_count > 0 );
+static void repetition_count_test_init ( struct entropy_source *source ) {
+	struct entropy_repetition_count_test *test =
+		&source->repetition_count_test;
 
-		return 0;
-	}
-
-	/* Find the first working source */
-	rc = -ENOENT;
-	for_each_table_entry ( entropy_source, ENTROPY_SOURCES ) {
-		if ( ( rc = entropy_enable() ) == 0 ) {
-			DBGC ( &entropy_source, "ENTROPY using source \"%s\"\n",
-			       entropy_source->name );
-			break;
-		}
-	}
-	return rc;
-}
-
-/**
- * Disable entropy gathering
- *
- */
-void entropy_disable ( void ) {
-
-	/* Sanity check */
-	assert ( entropy_source != NULL );
-
-	/* Disable entropy gathering, if applicable */
-	if ( entropy_source->disable )
-		entropy_source->disable();
+	/* Sanity checks */
+	assert ( test->repetition_count == 0 );
+	assert ( test->cutoff > 0 );
 }
 
 /**
  * Perform repetition count test
  *
+ * @v source		Entropy source
  * @v sample		Noise sample
  * @ret rc		Return status code
  *
  * This is the Repetition Count Test defined in ANS X9.82 Part 2
  * (October 2011 Draft) Section 8.5.2.1.2.
  */
-static int repetition_count_test ( noise_sample_t sample ) {
-	static noise_sample_t most_recent_sample;
-	static unsigned int repetition_count = 0;
-	unsigned int repetition_count_cutoff =
-		entropy_source->repetition_count_cutoff;
+static int repetition_count_test ( struct entropy_source *source,
+				   noise_sample_t sample ) {
+	struct entropy_repetition_count_test *test =
+		&source->repetition_count_test;
 
 	/* A = the most recently seen sample value
 	 * B = the number of times that value A has been seen in a row
@@ -133,49 +90,71 @@ static int repetition_count_test ( noise_sample_t sample ) {
 	 * the initial value of most_recent_sample is treated as being
 	 * undefined.)
 	 */
-	if ( ( sample == most_recent_sample ) && ( repetition_count > 0 ) ) {
+	if ( ( sample == test->most_recent_sample ) &&
+	     ( test->repetition_count > 0 ) ) {
 
 		/* a) If the new sample = A, then B is incremented by one. */
-		repetition_count++;
+		test->repetition_count++;
 
 		/*    i.  If B >= C, then an error condition is raised
 		 *        due to a failure of the test
 		 */
-		if ( repetition_count >= repetition_count_cutoff )
+		if ( test->repetition_count >= test->cutoff ) {
+			DBGC ( source, "ENTROPY %s excessively repeated "
+			       "value %d (%d/%d)\n", source->name, sample,
+			       test->repetition_count, test->cutoff );
 			return -EPIPE_REPETITION_COUNT_TEST;
+		}
 
 	} else {
 
 		/* b) Else:
 		 *    i.  A = new sample
 		 */
-		most_recent_sample = sample;
+		test->most_recent_sample = sample;
 
 		/*    ii. B = 1 */
-		repetition_count = 1;
+		test->repetition_count = 1;
 	}
 
 	return 0;
 }
 
 /**
+ * Initialise adaptive proportion test
+ *
+ * @v source		Entropy source
+ */
+static void adaptive_proportion_test_init ( struct entropy_source *source ) {
+	struct entropy_adaptive_proportion_test *test =
+		&source->adaptive_proportion_test;
+
+	/* Sanity checks */
+	assert ( test->sample_count == 0 );
+	assert ( test->repetition_count == 0 );
+	assert ( test->cutoff > 0 );
+
+	/* Ensure that a new test run starts immediately */
+	test->sample_count = ADAPTIVE_PROPORTION_WINDOW_SIZE;
+}
+
+/**
  * Perform adaptive proportion test
  *
+ * @v source		Entropy source
  * @v sample		Noise sample
  * @ret rc		Return status code
  *
  * This is the Adaptive Proportion Test for the Most Common Value
  * defined in ANS X9.82 Part 2 (October 2011 Draft) Section 8.5.2.1.3.
  */
-static int adaptive_proportion_test ( noise_sample_t sample ) {
-	static noise_sample_t current_counted_sample;
-	static unsigned int sample_count = ADAPTIVE_PROPORTION_WINDOW_SIZE;
-	static unsigned int repetition_count;
-	unsigned int adaptive_proportion_cutoff =
-		entropy_source->adaptive_proportion_cutoff;
+static int adaptive_proportion_test ( struct entropy_source *source,
+				      noise_sample_t sample ) {
+	struct entropy_adaptive_proportion_test *test =
+		&source->adaptive_proportion_test;
 
 	/* A = the sample value currently being counted
-	 * B = the number of samples examined in this run of the test so far
+	 * S = the number of samples examined in this run of the test so far
 	 * N = the total number of samples that must be observed in
 	 *     one run of the test, also known as the "window size" of
 	 *     the test
@@ -192,37 +171,41 @@ static int adaptive_proportion_test ( noise_sample_t sample ) {
 	 */
 
 	/* 2.  If S = N, then a new run of the test begins: */
-	if ( sample_count == ADAPTIVE_PROPORTION_WINDOW_SIZE ) {
+	if ( test->sample_count == ADAPTIVE_PROPORTION_WINDOW_SIZE ) {
 
 		/* a.  A = the current sample */
-		current_counted_sample = sample;
+		test->current_counted_sample = sample;
 
 		/* b.  S = 0 */
-		sample_count = 0;
+		test->sample_count = 0;
 
 		/* c. B = 0 */
-		repetition_count = 0;
+		test->repetition_count = 0;
 
 	} else {
 
 		/* Else: (the test is already running)
 		 * a.  S = S + 1
 		 */
-		sample_count++;
+		test->sample_count++;
 
 		/* b.  If A = the current sample, then: */
-		if ( sample == current_counted_sample ) {
+		if ( sample == test->current_counted_sample ) {
 
 			/* i.   B = B + 1 */
-			repetition_count++;
+			test->repetition_count++;
 
 			/* ii.  If S (sic) > C then raise an error
 			 *      condition, because the test has
 			 *      detected a failure
 			 */
-			if ( repetition_count > adaptive_proportion_cutoff )
+			if ( test->repetition_count > test->cutoff ) {
+				DBGC ( source, "ENTROPY %s excessively "
+				       "repeated value %d (%d/%d)\n",
+				       source->name, sample,
+				       test->repetition_count, test->cutoff );
 				return -EPIPE_ADAPTIVE_PROPORTION_TEST;
-
+			}
 		}
 	}
 
@@ -230,59 +213,182 @@ static int adaptive_proportion_test ( noise_sample_t sample ) {
 }
 
 /**
- * Get noise sample
- *
- * @ret noise		Noise sample
- * @ret rc		Return status code
- *
- * This is the GetNoise function defined in ANS X9.82 Part 2
- * (October 2011 Draft) Section 6.5.2.
- */
-int get_noise ( noise_sample_t *noise ) {
-
-	/* Sanity check */
-	assert ( entropy_source != NULL );
-
-	return entropy_source->get_noise ( noise );
-}
-
-/**
  * Get entropy sample
  *
+ * @v source		Entropy source
  * @ret entropy		Entropy sample
  * @ret rc		Return status code
  *
  * This is the GetEntropy function defined in ANS X9.82 Part 2
  * (October 2011 Draft) Section 6.5.1.
  */
-static int get_entropy ( entropy_sample_t *entropy ) {
-	static int rc = 0;
+static int get_entropy ( struct entropy_source *source,
+			 entropy_sample_t *entropy ) {
 	noise_sample_t noise;
-
-	/* Sanity check */
-	assert ( entropy_source != NULL );
+	int rc;
 
 	/* Any failure is permanent */
-	if ( rc != 0 )
-		return rc;
+	if ( ( rc = source->rc ) != 0 )
+		goto err_broken;
 
 	/* Get noise sample */
-	if ( ( rc = get_noise ( &noise ) ) != 0 )
-		return rc;
+	if ( ( rc = get_noise ( source, &noise ) ) != 0 )
+		goto err_get_noise;
 
 	/* Perform Repetition Count Test and Adaptive Proportion Test
 	 * as mandated by ANS X9.82 Part 2 (October 2011 Draft)
 	 * Section 8.5.2.1.1.
 	 */
-	if ( ( rc = repetition_count_test ( noise ) ) != 0 )
-		return rc;
-	if ( ( rc = adaptive_proportion_test ( noise ) ) != 0 )
-		return rc;
+	if ( ( rc = repetition_count_test ( source, noise ) ) != 0 )
+		goto err_repetition_count_test;
+	if ( ( rc = adaptive_proportion_test ( source, noise ) ) != 0 )
+		goto err_adaptive_proportion_test;
 
 	/* We do not use any optional conditioning component */
 	*entropy = noise;
 
 	return 0;
+
+ err_adaptive_proportion_test:
+ err_repetition_count_test:
+ err_get_noise:
+	source->rc = rc;
+ err_broken:
+	return rc;
+}
+
+/**
+ * Initialise startup test
+ *
+ * @v source		Entropy source
+ */
+static void startup_test_init ( struct entropy_source *source ) {
+	struct entropy_startup_test *test = &source->startup_test;
+
+	/* Sanity check */
+	assert ( test->tested == 0 );
+	assert ( test->count > 0 );
+}
+
+/**
+ * Perform startup test
+ *
+ * @v source		Entropy source
+ * @ret rc		Return status code
+ */
+static int startup_test ( struct entropy_source *source ) {
+	struct entropy_startup_test *test = &source->startup_test;
+	entropy_sample_t sample;
+	int rc;
+
+	/* Perform mandatory number of startup tests */
+	for ( ; test->tested < test->count ; test->tested++ ) {
+		if ( ( rc = get_entropy ( source, &sample ) ) != 0 ) {
+			DBGC ( source, "ENTROPY %s failed: %s\n",
+			       source->name, strerror ( rc ) );
+			return rc;
+		}
+	}
+
+	return 0;
+}
+
+/**
+ * Enable entropy gathering
+ *
+ * @v source		Entropy source
+ * @ret rc		Return status code
+ */
+int entropy_enable ( struct entropy_source *source ) {
+	int rc;
+
+	/* Refuse to enable a previously failed source */
+	if ( ( rc = source->rc ) != 0 )
+		return rc;
+
+	/* Enable entropy source */
+	if ( ( rc = source->enable() ) != 0 ) {
+		DBGC ( source, "ENTROPY %s could not enable: %s\n",
+		       source->name, strerror ( rc ) );
+		source->rc = rc;
+		return rc;
+	}
+
+	/* Sanity check */
+	assert ( source->min_entropy_per_sample > 0 );
+
+	/* Initialise test state if this source has not previously been used */
+	if ( source->startup_test.tested == 0 ) {
+		repetition_count_test_init ( source );
+		adaptive_proportion_test_init ( source );
+		startup_test_init ( source );
+	}
+
+	DBGC ( source, "ENTROPY %s enabled\n", source->name );
+	return 0;
+}
+
+/**
+ * Enable and test entropy source
+ *
+ * @v source		Entropy source
+ * @ret rc		Return status code
+ */
+static int entropy_enable_and_test ( struct entropy_source *source ) {
+	int rc;
+
+	/* Enable source */
+	if ( ( rc = entropy_enable ( source ) ) != 0 )
+		goto err_enable;
+
+	/* Test source */
+	if ( ( rc = startup_test ( source ) ) != 0 )
+		goto err_test;
+
+	DBGC ( source, "ENTROPY %s passed %d startup tests\n",
+	       source->name, source->startup_test.count );
+	return 0;
+
+ err_test:
+	entropy_disable ( source );
+ err_enable:
+	assert ( source->rc == rc );
+	return rc;
+}
+
+/**
+ * Enable first working entropy source
+ *
+ * @v source		Entropy source to fill in
+ * @ret rc		Return status code
+ */
+static int entropy_enable_working ( struct entropy_source **source ) {
+	int rc;
+
+	/* Find the first working source */
+	rc = -ENOENT;
+	for_each_table_entry ( *source, ENTROPY_SOURCES ) {
+		if ( ( rc = entropy_enable_and_test ( *source ) ) == 0 )
+			return 0;
+	}
+
+	DBGC ( *source, "ENTROPY has no working sources: %s\n",
+	       strerror ( rc ) );
+	return rc;
+}
+
+/**
+ * Disable entropy gathering
+ *
+ * @v source		Entropy source
+ */
+void entropy_disable ( struct entropy_source *source ) {
+
+	/* Disable entropy gathering, if applicable */
+	if ( source->disable )
+		source->disable();
+
+	DBGC ( source, "ENTROPY %s disabled\n", source->name );
 }
 
 /**
@@ -318,7 +424,7 @@ static uint32_t make_next_nonce ( void ) {
  */
 int get_entropy_input_tmp ( min_entropy_t min_entropy, uint8_t *tmp,
 			    size_t tmp_len ) {
-	static unsigned int startup_tested = 0;
+	struct entropy_source *source;
 	struct {
 		uint32_t nonce;
 		entropy_sample_t sample;
@@ -330,15 +436,12 @@ int get_entropy_input_tmp ( min_entropy_t min_entropy, uint8_t *tmp,
 	int rc;
 
 	/* Enable entropy gathering */
-	if ( ( rc = entropy_enable() ) != 0 )
-		return rc;
+	if ( ( rc = entropy_enable_working ( &source ) ) != 0 )
+		goto err_enable_working;
 
-	/* Perform mandatory startup tests, if not yet performed */
-	for ( ; startup_tested < entropy_source->startup_test_count ;
-	      startup_tested++ ) {
-		if ( ( rc = get_entropy ( &data.sample ) ) != 0 )
-			goto err_get_entropy;
-	}
+	/* Sanity checks */
+	assert ( source->startup_test.count > 0 );
+	assert ( source->startup_test.tested >= source->startup_test.count );
 
 	/* 3.  entropy_total = 0 */
 	entropy_total = MIN_ENTROPY ( 0 );
@@ -352,7 +455,7 @@ int get_entropy_input_tmp ( min_entropy_t min_entropy, uint8_t *tmp,
 		 *       = GetEntropy()
 		 * 5.2.  If status indicates an error, return ( status, Null )
 		 */
-		if ( ( rc = get_entropy ( &data.sample ) ) != 0 )
+		if ( ( rc = get_entropy ( source, &data.sample ) ) != 0 )
 			goto err_get_entropy;
 
 		/* 5.3.  nonce = MakeNextNonce() */
@@ -367,18 +470,20 @@ int get_entropy_input_tmp ( min_entropy_t min_entropy, uint8_t *tmp,
 			tmp[i] ^= df_buf[i];
 
 		/* 5.5.  entropy_total = entropy_total + assessed_entropy */
-		entropy_total += entropy_source->min_entropy_per_sample;
+		entropy_total += source->min_entropy_per_sample;
 	}
 
 	/* Disable entropy gathering */
-	entropy_disable();
+	entropy_disable ( source );
 
-	DBGC ( &entropy_source, "ENTROPY gathered %d bits in %d samples\n",
-	       ( min_entropy / MIN_ENTROPY_SCALE ), num_samples );
+	DBGC ( source, "ENTROPY %s gathered %d bits in %d samples\n",
+	       source->name, ( min_entropy / MIN_ENTROPY_SCALE ), num_samples );
 	return 0;
 
  err_get_entropy:
-	entropy_disable();
+	entropy_disable ( source );
+	assert ( source->rc == rc );
+ err_enable_working:
 	return rc;
 }