[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, 102 insertions, 31 deletions

diff --git a/src/include/ipxe/entropy.h b/src/include/ipxe/entropy.h
index 108c3766..240feace 100644
--- a/src/include/ipxe/entropy.h
+++ b/src/include/ipxe/entropy.h
@@ -42,6 +42,76 @@ typedef unsigned int min_entropy_t;
 #define MIN_ENTROPY( bits ) \
 	( ( min_entropy_t ) ( (bits) * MIN_ENTROPY_SCALE ) )
 
+/**
+ * Repetition count test state
+ *
+ * This is the state for the repetition Count Test defined in ANS
+ * X9.82 Part 2 (October 2011 Draft) Section 8.5.2.1.2.
+ */
+struct entropy_repetition_count_test {
+	/**
+	 * A = the most recently seen sample value
+	 */
+	noise_sample_t most_recent_sample;
+	/**
+	 * B = the number of times that value A has been seen in a row
+	 */
+	unsigned int repetition_count;
+	/**
+	 * C = the cutoff value above which the repetition test should fail
+	 *
+	 * Filled in by entropy_init().
+	 */
+	unsigned int cutoff;
+};
+
+/**
+ * Adaptive proportion test state
+ *
+ * This is the state for 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.
+ */
+struct entropy_adaptive_proportion_test {
+	/**
+	 * A = the sample value currently being counted
+	 */
+	noise_sample_t current_counted_sample;
+	/**
+	 * S = the number of samples examined in this run of the test so far
+	 */
+	unsigned int sample_count;
+	/**
+	 * B = the current number of times that S (sic) has been seen
+	 *     in the W (sic) samples examined so far
+	 */
+	unsigned int repetition_count;
+	/**
+	 * C = the cutoff value above which the repetition test should fail
+	 *
+	 * Filled in by entropy_init().
+	 */
+	unsigned int cutoff;
+};
+
+/**
+ * Startup test state
+ *
+ * ANS X9.82 Part 2 (October 2011 Draft) Section 8.5.2.1.5 requires
+ * that at least one full cycle of the continuous tests must be
+ * performed at start-up.
+ */
+struct entropy_startup_test {
+	/** Number of startup tests performed */
+	unsigned int tested;
+	/**
+	 * Number of startup tests required for one full cycle
+	 *
+	 * Filled in by entropy_init().
+	 */
+	unsigned int count;
+};
+
 /** An entropy source */
 struct entropy_source {
 	/** Name */
@@ -59,34 +129,19 @@ struct entropy_source {
 	 * Filled in by entropy_init().
 	 */
 	min_entropy_t min_entropy_per_sample;
+	/** Repetition count test state */
+	struct entropy_repetition_count_test repetition_count_test;
+	/** Adaptive proportion test state */
+	struct entropy_adaptive_proportion_test adaptive_proportion_test;
+	/** Startup test state */
+	struct entropy_startup_test startup_test;
 	/**
-	 * Repetition count test cutoff value
-	 *
-	 * This is the cutoff value for the Repetition Count Test
-	 * defined in ANS X9.82 Part 2 (October 2011 Draft) Section
-	 * 8.5.2.1.2.
-	 *
-	 * Filled in by entropy_init().
-	 */
-	unsigned int repetition_count_cutoff;
-	/**
-	 * Adaptive proportion test cutoff value
-	 *
-	 * This is the cutoff value for the Adaptive Proportion Test
-	 * defined in ANS X9.82 Part 2 (October 2011 Draft) Section
-	 * 8.5.2.1.3.1.2.
-	 *
-	 * Filled in by entropy_init().
-	 */
-	unsigned int adaptive_proportion_cutoff;
-	/**
-	 * Startup test count
+	 * Failure status (if any)
 	 *
-	 * ANS X9.82 Part 2 (October 2011 Draft) Section 8.5.2.1.5
-	 * requires that at least one full cycle of the continuous
-	 * tests must be performed at start-up.
+	 * Any failure of an entropy source is regarded as permanent.
 	 */
-	unsigned int startup_test_count;
+	int rc;
+
 	/**
 	 * Enable entropy gathering
 	 *
@@ -140,6 +195,22 @@ extern int get_entropy_input_tmp ( min_entropy_t min_entropy, uint8_t *tmp,
 #define ENTROPY_HASH_DF_OUTLEN_BYTES SHA256_DIGEST_SIZE
 
 /**
+ * Get noise sample
+ *
+ * @v source		Entropy source
+ * @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.
+ */
+static inline __attribute__ (( always_inline )) int
+get_noise ( struct entropy_source *source, noise_sample_t *noise ) {
+
+	return source->get_noise ( noise );
+}
+
+/**
  * Obtain entropy input
  *
  * @v min_entropy_bits	Minimum amount of entropy, in bits
@@ -445,13 +516,13 @@ entropy_init ( struct entropy_source *source,
 
 	/* Record min-entropy per sample and test cutoff values */
 	source->min_entropy_per_sample = min_entropy_per_sample;
-	source->repetition_count_cutoff = repetition_count_cutoff;
-	source->adaptive_proportion_cutoff = adaptive_proportion_cutoff;
-	source->startup_test_count = startup_test_count;
+	source->repetition_count_test.cutoff = repetition_count_cutoff;
+	source->adaptive_proportion_test.cutoff = adaptive_proportion_cutoff;
+	source->startup_test.count = startup_test_count;
 }
 
-extern int entropy_enable ( void );
-extern void entropy_disable ( void );
-extern int get_noise ( noise_sample_t *noise );
+extern int entropy_enable ( struct entropy_source *source );
+extern void entropy_disable ( struct entropy_source *source );
+extern int get_noise ( struct entropy_source *source, noise_sample_t *noise );
 
 #endif /* _IPXE_ENTROPY_H */