[PATCH v2 0/2] crypto: Jitter RNG SP800-90B compliance

[PATCH v2 0/2] crypto: Jitter RNG SP800-90B compliance

[Stephan Müller]

Hi,

This patch set adds SP800-90B compliance to the Jitter RNG. The
SP800-90B patch is tested for more than half a year in user space
with the Jitter RNG version 2.2.0.

The full SP800-90B assessment of the Jitter RNG is provided at [1].

In addition, the DRBG implementation is updated to always be
reseeded from the Jitter RNG. To ensure the DRBG is reseeded within
an appropriate amount of time, the reseed threshold is lowered.

Changes v2:
* Instead of free/alloc of the Jitter RNG instance in case of a health
  test error, re-initialize the RNG instance by performing the
  power-up test and after a success, clear the health test status and
  error.

[1] http://www.chronox.de/jent/doc/CPU-Jitter-NPTRNG.pdf

Stephan Mueller (2):
  crypto: Jitter RNG SP800-90B compliance
  crypto: DRBG always seeded with SP800-90B compliant noise source

 crypto/drbg.c                |  26 ++-
 crypto/jitterentropy-kcapi.c |  27 +++
 crypto/jitterentropy.c       | 417 ++++++++++++++++++++++++++---------
 include/crypto/drbg.h        |   6 +-
 4 files changed, 363 insertions(+), 113 deletions(-)

-- 
2.25.2

[PATCH v2 1/2] crypto: Jitter RNG SP800-90B compliance

[Stephan Müller]

SP800-90B specifies various requirements for the noise source(s) that
may seed any DRNG including SP800-90A DRBGs. In November 2020,
SP800-90B will be mandated for all noise sources that provide entropy
to DRBGs as part of a FIPS 140-[2|3] validation or other evaluation
types. Without SP800-90B compliance, a noise source is defined to always
deliver zero bits of entropy.

This patch ports the SP800-90B compliance from the user space Jitter RNG
version 2.2.0.

The following changes are applied:

- addition of (an enhanced version of) the repetitive count test (RCT)
  from SP800-90B section 4.4.1 - the enhancement is due to the fact of
  using the stuck test as input to the RCT.

- addition of the adaptive proportion test (APT) from SP800-90B section
  4.4.2

- update of the power-on self test to perform a test measurement of 1024
  noise samples compliant to SP800-90B section 4.3

- remove of the continuous random number generator test which is
  replaced by APT and RCT

Health test failures due to the SP800-90B operation are only enforced in
FIPS mode. If a runtime health test failure is detected, the Jitter RNG
is reset. If more than 1024 resets in a row are performed, a permanent
error is returned to the caller.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 crypto/jitterentropy-kcapi.c |  27 +++
 crypto/jitterentropy.c       | 417 ++++++++++++++++++++++++++---------
 2 files changed, 343 insertions(+), 101 deletions(-)

diff --git a/crypto/jitterentropy-kcapi.c b/crypto/jitterentropy-kcapi.c
index a5ce8f96790f..b43684c0dade 100644
--- a/crypto/jitterentropy-kcapi.c
+++ b/crypto/jitterentropy-kcapi.c
@@ -108,6 +108,7 @@ void jent_get_nstime(__u64 *out)
 struct jitterentropy {
 	spinlock_t jent_lock;
 	struct rand_data *entropy_collector;
+	unsigned int reset_cnt;
 };
 
 static int jent_kcapi_init(struct crypto_tfm *tfm)
@@ -142,7 +143,33 @@ static int jent_kcapi_random(struct crypto_rng *tfm,
 	int ret = 0;
 
 	spin_lock(&rng->jent_lock);
+
+	/* Return a permanent error in case we had too many resets in a row. */
+	if (rng->reset_cnt > (1<<10)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
 	ret = jent_read_entropy(rng->entropy_collector, rdata, dlen);
+
+	/* Reset RNG in case of health failures */
+	if (ret < -1) {
+		pr_warn_ratelimited("Reset Jitter RNG due to health test failure: %s failure\n",
+				    (ret == -2) ? "Repetition Count Test" :
+						  "Adaptive Proportion Test");
+
+		rng->reset_cnt++;
+
+		ret = -EAGAIN;
+	} else {
+		rng->reset_cnt = 0;
+
+		/* Convert the Jitter RNG error into a usable error code */
+		if (ret == -1)
+			ret = -EINVAL;
+	}
+
+out:
 	spin_unlock(&rng->jent_lock);
 
 	return ret;
diff --git a/crypto/jitterentropy.c b/crypto/jitterentropy.c
index 042157f0d28b..57f4a1ac738b 100644
--- a/crypto/jitterentropy.c
+++ b/crypto/jitterentropy.c
@@ -2,7 +2,7 @@
  * Non-physical true random number generator based on timing jitter --
  * Jitter RNG standalone code.
  *
- * Copyright Stephan Mueller <smueller@chronox.de>, 2015 - 2019
+ * Copyright Stephan Mueller <smueller@chronox.de>, 2015 - 2020
  *
  * Design
  * ======
@@ -47,7 +47,7 @@
 
 /*
  * This Jitterentropy RNG is based on the jitterentropy library
- * version 2.1.2 provided at http://www.chronox.de/jent.html
+ * version 2.2.0 provided at http://www.chronox.de/jent.html
  */
 
 #ifdef __OPTIMIZE__
@@ -83,6 +83,22 @@ struct rand_data {
 	unsigned int memblocksize; /* Size of one memory block in bytes */
 	unsigned int memaccessloops; /* Number of memory accesses per random
 				      * bit generation */
+
+	/* Repetition Count Test */
+	int rct_count;			/* Number of stuck values */
+
+	/* Adaptive Proportion Test for a significance level of 2^-30 */
+#define JENT_APT_CUTOFF		325	/* Taken from SP800-90B sec 4.4.2 */
+#define JENT_APT_WINDOW_SIZE	512	/* Data window size */
+	/* LSB of time stamp to process */
+#define JENT_APT_LSB		16
+#define JENT_APT_WORD_MASK	(JENT_APT_LSB - 1)
+	unsigned int apt_observations;	/* Number of collected observations */
+	unsigned int apt_count;		/* APT counter */
+	unsigned int apt_base;		/* APT base reference */
+	unsigned int apt_base_set:1;	/* APT base reference set? */
+
+	unsigned int health_failure:1;	/* Permanent health failure */
 };
 
 /* Flags that can be used to initialize the RNG */
@@ -98,12 +114,201 @@ struct rand_data {
 				   * variations (2nd derivation of time is
 				   * zero). */
 #define JENT_ESTUCK		8 /* Too many stuck results during init. */
+#define JENT_EHEALTH		9 /* Health test failed during initialization */
+#define JENT_ERCT		10 /* RCT failed during initialization */
+
+#include "jitterentropy.h"
 
 /***************************************************************************
- * Helper functions
+ * Adaptive Proportion Test
+ *
+ * This test complies with SP800-90B section 4.4.2.
  ***************************************************************************/
 
-#include "jitterentropy.h"
+/**
+ * Reset the APT counter
+ *
+ * @ec [in] Reference to entropy collector
+ */
+static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked)
+{
+	/* Reset APT counter */
+	ec->apt_count = 0;
+	ec->apt_base = delta_masked;
+	ec->apt_observations = 0;
+}
+
+/**
+ * Insert a new entropy event into APT
+ *
+ * @ec [in] Reference to entropy collector
+ * @delta_masked [in] Masked time delta to process
+ */
+static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked)
+{
+	/* Initialize the base reference */
+	if (!ec->apt_base_set) {
+		ec->apt_base = delta_masked;
+		ec->apt_base_set = 1;
+		return;
+	}
+
+	if (delta_masked == ec->apt_base) {
+		ec->apt_count++;
+
+		if (ec->apt_count >= JENT_APT_CUTOFF)
+			ec->health_failure = 1;
+	}
+
+	ec->apt_observations++;
+
+	if (ec->apt_observations >= JENT_APT_WINDOW_SIZE)
+		jent_apt_reset(ec, delta_masked);
+}
+
+/***************************************************************************
+ * Stuck Test and its use as Repetition Count Test
+ *
+ * The Jitter RNG uses an enhanced version of the Repetition Count Test
+ * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical
+ * back-to-back values, the input to the RCT is the counting of the stuck
+ * values during the generation of one Jitter RNG output block.
+ *
+ * The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8.
+ *
+ * During the counting operation, the Jitter RNG always calculates the RCT
+ * cut-off value of C. If that value exceeds the allowed cut-off value,
+ * the Jitter RNG output block will be calculated completely but discarded at
+ * the end. The caller of the Jitter RNG is informed with an error code.
+ ***************************************************************************/
+
+/**
+ * Repetition Count Test as defined in SP800-90B section 4.4.1
+ *
+ * @ec [in] Reference to entropy collector
+ * @stuck [in] Indicator whether the value is stuck
+ */
+static void jent_rct_insert(struct rand_data *ec, int stuck)
+{
+	/*
+	 * If we have a count less than zero, a previous RCT round identified
+	 * a failure. We will not overwrite it.
+	 */
+	if (ec->rct_count < 0)
+		return;
+
+	if (stuck) {
+		ec->rct_count++;
+
+		/*
+		 * The cutoff value is based on the following consideration:
+		 * alpha = 2^-30 as recommended in FIPS 140-2 IG 9.8.
+		 * In addition, we require an entropy value H of 1/OSR as this
+		 * is the minimum entropy required to provide full entropy.
+		 * Note, we collect 64 * OSR deltas for inserting them into
+		 * the entropy pool which should then have (close to) 64 bits
+		 * of entropy.
+		 *
+		 * Note, ec->rct_count (which equals to value B in the pseudo
+		 * code of SP800-90B section 4.4.1) starts with zero. Hence
+		 * we need to subtract one from the cutoff value as calculated
+		 * following SP800-90B.
+		 */
+		if ((unsigned int)ec->rct_count >= (31 * ec->osr)) {
+			ec->rct_count = -1;
+			ec->health_failure = 1;
+		}
+	} else {
+		ec->rct_count = 0;
+	}
+}
+
+/**
+ * Is there an RCT health test failure?
+ *
+ * @ec [in] Reference to entropy collector
+ *
+ * @return
+ * 	0 No health test failure
+ * 	1 Permanent health test failure
+ */
+static int jent_rct_failure(struct rand_data *ec)
+{
+	if (ec->rct_count < 0)
+		return 1;
+	return 0;
+}
+
+static inline __u64 jent_delta(__u64 prev, __u64 next)
+{
+#define JENT_UINT64_MAX		(__u64)(~((__u64) 0))
+	return (prev < next) ? (next - prev) :
+			       (JENT_UINT64_MAX - prev + 1 + next);
+}
+
+/**
+ * Stuck test by checking the:
+ * 	1st derivative of the jitter measurement (time delta)
+ * 	2nd derivative of the jitter measurement (delta of time deltas)
+ * 	3rd derivative of the jitter measurement (delta of delta of time deltas)
+ *
+ * All values must always be non-zero.
+ *
+ * @ec [in] Reference to entropy collector
+ * @current_delta [in] Jitter time delta
+ *
+ * @return
+ * 	0 jitter measurement not stuck (good bit)
+ * 	1 jitter measurement stuck (reject bit)
+ */
+static int jent_stuck(struct rand_data *ec, __u64 current_delta)
+{
+	__u64 delta2 = jent_delta(ec->last_delta, current_delta);
+	__u64 delta3 = jent_delta(ec->last_delta2, delta2);
+	unsigned int delta_masked = current_delta & JENT_APT_WORD_MASK;
+
+	ec->last_delta = current_delta;
+	ec->last_delta2 = delta2;
+
+	/*
+	 * Insert the result of the comparison of two back-to-back time
+	 * deltas.
+	 */
+	jent_apt_insert(ec, delta_masked);
+
+	if (!current_delta || !delta2 || !delta3) {
+		/* RCT with a stuck bit */
+		jent_rct_insert(ec, 1);
+		return 1;
+	}
+
+	/* RCT with a non-stuck bit */
+	jent_rct_insert(ec, 0);
+
+	return 0;
+}
+
+/**
+ * Report any health test failures
+ *
+ * @ec [in] Reference to entropy collector
+ *
+ * @return
+ * 	0 No health test failure
+ * 	1 Permanent health test failure
+ */
+static int jent_health_failure(struct rand_data *ec)
+{
+	/* Test is only enabled in FIPS mode */
+	if (!jent_fips_enabled())
+		return 0;
+
+	return ec->health_failure;
+}
+
+/***************************************************************************
+ * Noise sources
+ ***************************************************************************/
 
 /**
  * Update of the loop count used for the next round of
@@ -148,10 +353,6 @@ static __u64 jent_loop_shuffle(struct rand_data *ec,
 	return (shuffle + (1<<min));
 }
 
-/***************************************************************************
- * Noise sources
- ***************************************************************************/
-
 /**
  * CPU Jitter noise source -- this is the noise source based on the CPU
  *			      execution time jitter
@@ -166,18 +367,19 @@ static __u64 jent_loop_shuffle(struct rand_data *ec,
  * the CPU execution time jitter. Any change to the loop in this function
  * implies that careful retesting must be done.
  *
- * Input:
- * @ec entropy collector struct
- * @time time stamp to be injected
- * @loop_cnt if a value not equal to 0 is set, use the given value as number of
- *	     loops to perform the folding
+ * @ec [in] entropy collector struct
+ * @time [in] time stamp to be injected
+ * @loop_cnt [in] if a value not equal to 0 is set, use the given value as
+ *		  number of loops to perform the folding
+ * @stuck [in] Is the time stamp identified as stuck?
  *
  * Output:
  * updated ec->data
  *
  * @return Number of loops the folding operation is performed
  */
-static __u64 jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt)
+static void jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt,
+			   int stuck)
 {
 	unsigned int i;
 	__u64 j = 0;
@@ -220,9 +422,17 @@ static __u64 jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt)
 			new ^= tmp;
 		}
 	}
-	ec->data = new;
 
-	return fold_loop_cnt;
+	/*
+	 * If the time stamp is stuck, do not finally insert the value into
+	 * the entropy pool. Although this operation should not do any harm
+	 * even when the time stamp has no entropy, SP800-90B requires that
+	 * any conditioning operation (SP800-90B considers the LFSR to be a
+	 * conditioning operation) to have an identical amount of input
+	 * data according to section 3.1.5.
+	 */
+	if (!stuck)
+		ec->data = new;
 }
 
 /**
@@ -243,16 +453,13 @@ static __u64 jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt)
  * to reliably access either L3 or memory, the ec->mem memory must be quite
  * large which is usually not desirable.
  *
- * Input:
- * @ec Reference to the entropy collector with the memory access data -- if
- *     the reference to the memory block to be accessed is NULL, this noise
- *     source is disabled
- * @loop_cnt if a value not equal to 0 is set, use the given value as number of
- *	     loops to perform the folding
- *
- * @return Number of memory access operations
+ * @ec [in] Reference to the entropy collector with the memory access data -- if
+ *	    the reference to the memory block to be accessed is NULL, this noise
+ *	    source is disabled
+ * @loop_cnt [in] if a value not equal to 0 is set, use the given value
+ *		  number of loops to perform the LFSR
  */
-static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
+static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
 {
 	unsigned int wrap = 0;
 	__u64 i = 0;
@@ -262,7 +469,7 @@ static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
 		jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT);
 
 	if (NULL == ec || NULL == ec->mem)
-		return 0;
+		return;
 	wrap = ec->memblocksize * ec->memblocks;
 
 	/*
@@ -288,43 +495,11 @@ static unsigned int jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
 		ec->memlocation = ec->memlocation + ec->memblocksize - 1;
 		ec->memlocation = ec->memlocation % wrap;
 	}
-	return i;
 }
 
 /***************************************************************************
  * Start of entropy processing logic
  ***************************************************************************/
-
-/**
- * Stuck test by checking the:
- *	1st derivation of the jitter measurement (time delta)
- *	2nd derivation of the jitter measurement (delta of time deltas)
- *	3rd derivation of the jitter measurement (delta of delta of time deltas)
- *
- * All values must always be non-zero.
- *
- * Input:
- * @ec Reference to entropy collector
- * @current_delta Jitter time delta
- *
- * @return
- *	0 jitter measurement not stuck (good bit)
- *	1 jitter measurement stuck (reject bit)
- */
-static int jent_stuck(struct rand_data *ec, __u64 current_delta)
-{
-	__s64 delta2 = ec->last_delta - current_delta;
-	__s64 delta3 = delta2 - ec->last_delta2;
-
-	ec->last_delta = current_delta;
-	ec->last_delta2 = delta2;
-
-	if (!current_delta || !delta2 || !delta3)
-		return 1;
-
-	return 0;
-}
-
 /**
  * This is the heart of the entropy generation: calculate time deltas and
  * use the CPU jitter in the time deltas. The jitter is injected into the
@@ -334,8 +509,7 @@ static int jent_stuck(struct rand_data *ec, __u64 current_delta)
  *	    of this function! This can be done by calling this function
  *	    and not using its result.
  *
- * Input:
- * @entropy_collector Reference to entropy collector
+ * @ec [in] Reference to entropy collector
  *
  * @return result of stuck test
  */
@@ -343,6 +517,7 @@ static int jent_measure_jitter(struct rand_data *ec)
 {
 	__u64 time = 0;
 	__u64 current_delta = 0;
+	int stuck;
 
 	/* Invoke one noise source before time measurement to add variations */
 	jent_memaccess(ec, 0);
@@ -352,22 +527,23 @@ static int jent_measure_jitter(struct rand_data *ec)
 	 * invocation to measure the timing variations
 	 */
 	jent_get_nstime(&time);
-	current_delta = time - ec->prev_time;
+	current_delta = jent_delta(ec->prev_time, time);
 	ec->prev_time = time;
 
+	/* Check whether we have a stuck measurement. */
+	stuck = jent_stuck(ec, current_delta);
+
 	/* Now call the next noise sources which also injects the data */
-	jent_lfsr_time(ec, current_delta, 0);
+	jent_lfsr_time(ec, current_delta, 0, stuck);
 
-	/* Check whether we have a stuck measurement. */
-	return jent_stuck(ec, current_delta);
+	return stuck;
 }
 
 /**
  * Generator of one 64 bit random number
  * Function fills rand_data->data
  *
- * Input:
- * @ec Reference to entropy collector
+ * @ec [in] Reference to entropy collector
  */
 static void jent_gen_entropy(struct rand_data *ec)
 {
@@ -390,31 +566,6 @@ static void jent_gen_entropy(struct rand_data *ec)
 	}
 }
 
-/**
- * The continuous test required by FIPS 140-2 -- the function automatically
- * primes the test if needed.
- *
- * Return:
- * returns normally if FIPS test passed
- * panics the kernel if FIPS test failed
- */
-static void jent_fips_test(struct rand_data *ec)
-{
-	if (!jent_fips_enabled())
-		return;
-
-	/* prime the FIPS test */
-	if (!ec->old_data) {
-		ec->old_data = ec->data;
-		jent_gen_entropy(ec);
-	}
-
-	if (ec->data == ec->old_data)
-		jent_panic("jitterentropy: Duplicate output detected\n");
-
-	ec->old_data = ec->data;
-}
-
 /**
  * Entry function: Obtain entropy for the caller.
  *
@@ -425,17 +576,18 @@ static void jent_fips_test(struct rand_data *ec)
  * This function truncates the last 64 bit entropy value output to the exact
  * size specified by the caller.
  *
- * Input:
- * @ec Reference to entropy collector
- * @data pointer to buffer for storing random data -- buffer must already
- *	 exist
- * @len size of the buffer, specifying also the requested number of random
- *	in bytes
+ * @ec [in] Reference to entropy collector
+ * @data [in] pointer to buffer for storing random data -- buffer must already
+ *	      exist
+ * @len [in] size of the buffer, specifying also the requested number of random
+ *	     in bytes
  *
  * @return 0 when request is fulfilled or an error
  *
  * The following error codes can occur:
  *	-1	entropy_collector is NULL
+ *	-2	RCT failed
+ *	-3	APT test failed
  */
 int jent_read_entropy(struct rand_data *ec, unsigned char *data,
 		      unsigned int len)
@@ -449,7 +601,42 @@ int jent_read_entropy(struct rand_data *ec, unsigned char *data,
 		unsigned int tocopy;
 
 		jent_gen_entropy(ec);
-		jent_fips_test(ec);
+
+		if (jent_health_failure(ec)) {
+			int ret;
+
+			if (jent_rct_failure(ec))
+				ret = -2;
+			else
+				ret = -3;
+
+			/*
+			 * Re-initialize the noise source
+			 *
+			 * If the health test fails, the Jitter RNG remains
+			 * in failure state and will return a health failure
+			 * during next invocation.
+			 */
+			if (jent_entropy_init())
+				return ret;
+
+			/* Set APT to initial state */
+			jent_apt_reset(ec, 0);
+			ec->apt_base_set = 0;
+
+			/* Set RCT to initial state */
+			ec->rct_count = 0;
+
+			/* Re-enable Jitter RNG */
+			ec->health_failure = 0;
+
+			/*
+			 * Return the health test failure status to the
+			 * caller as the generated value is not appropriate.
+			 */
+			return ret;
+		}
+
 		if ((DATA_SIZE_BITS / 8) < len)
 			tocopy = (DATA_SIZE_BITS / 8);
 		else
@@ -513,11 +700,15 @@ int jent_entropy_init(void)
 	int i;
 	__u64 delta_sum = 0;
 	__u64 old_delta = 0;
+	unsigned int nonstuck = 0;
 	int time_backwards = 0;
 	int count_mod = 0;
 	int count_stuck = 0;
 	struct rand_data ec = { 0 };
 
+	/* Required for RCT */
+	ec.osr = 1;
+
 	/* We could perform statistical tests here, but the problem is
 	 * that we only have a few loop counts to do testing. These
 	 * loop counts may show some slight skew and we produce
@@ -539,8 +730,10 @@ int jent_entropy_init(void)
 	/*
 	 * TESTLOOPCOUNT needs some loops to identify edge systems. 100 is
 	 * definitely too little.
+	 *
+	 * SP800-90B requires at least 1024 initial test cycles.
 	 */
-#define TESTLOOPCOUNT 300
+#define TESTLOOPCOUNT 1024
 #define CLEARCACHE 100
 	for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
 		__u64 time = 0;
@@ -552,13 +745,13 @@ int jent_entropy_init(void)
 		/* Invoke core entropy collection logic */
 		jent_get_nstime(&time);
 		ec.prev_time = time;
-		jent_lfsr_time(&ec, time, 0);
+		jent_lfsr_time(&ec, time, 0, 0);
 		jent_get_nstime(&time2);
 
 		/* test whether timer works */
 		if (!time || !time2)
 			return JENT_ENOTIME;
-		delta = time2 - time;
+		delta = jent_delta(time, time2);
 		/*
 		 * test whether timer is fine grained enough to provide
 		 * delta even when called shortly after each other -- this
@@ -581,6 +774,28 @@ int jent_entropy_init(void)
 
 		if (stuck)
 			count_stuck++;
+		else {
+			nonstuck++;
+
+			/*
+			 * Ensure that the APT succeeded.
+			 *
+			 * With the check below that count_stuck must be less
+			 * than 10% of the overall generated raw entropy values
+			 * it is guaranteed that the APT is invoked at
+			 * floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times.
+			 */
+			if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) {
+				jent_apt_reset(&ec,
+					       delta & JENT_APT_WORD_MASK);
+				if (jent_health_failure(&ec))
+					return JENT_EHEALTH;
+			}
+		}
+
+		/* Validate RCT */
+		if (jent_rct_failure(&ec))
+			return JENT_ERCT;
 
 		/* test whether we have an increasing timer */
 		if (!(time2 > time))
-- 
2.25.2

[PATCH v2 2/2] crypto: DRBG always seeded with SP800-90B compliant noise source

[Stephan Müller]

As the Jitter RNG provides an SP800-90B compliant noise source, use this
noise source always for the (re)seeding of the DRBG.

To make sure the DRBG is always properly seeded, the reseed threshold
is reduced to 1<<20 generate operations.

The Jitter RNG may report health test failures. Such health test
failures are treated as transient as follows. The DRBG will not reseed
from the Jitter RNG (but from get_random_bytes) in case of a health
test failure. Though, it produces the requested random number.

The Jitter RNG has a failure counter where at most 1024 consecutive
resets due to a health test failure are considered as a transient error.
If more consecutive resets are required, the Jitter RNG will return
a permanent error which is returned to the caller by the DRBG. With this
approach, the worst case reseed threshold is significantly lower than
mandated by SP800-90A in order to seed with an SP800-90B noise source:
the DRBG has a reseed threshold of 2^20 * 1024 = 2^30 generate requests.

Yet, in case of a transient Jitter RNG health test failure, the DRBG is
seeded with the data obtained from get_random_bytes.

However, if the Jitter RNG fails during the initial seeding operation
even due to a health test error, the DRBG will send an error to the
caller because at that time, the DRBG has received no seed that is
SP800-90B compliant.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 crypto/drbg.c         | 26 +++++++++++++++++++-------
 include/crypto/drbg.h |  6 +-----
 2 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/crypto/drbg.c b/crypto/drbg.c
index b6929eb5f565..e57901d8545b 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -1087,10 +1087,6 @@ static void drbg_async_seed(struct work_struct *work)
 	if (ret)
 		goto unlock;
 
-	/* If nonblocking pool is initialized, deactivate Jitter RNG */
-	crypto_free_rng(drbg->jent);
-	drbg->jent = NULL;
-
 	/* Set seeded to false so that if __drbg_seed fails the
 	 * next generate call will trigger a reseed.
 	 */
@@ -1168,7 +1164,23 @@ static int drbg_seed(struct drbg_state *drbg, struct drbg_string *pers,
 						   entropylen);
 			if (ret) {
 				pr_devel("DRBG: jent failed with %d\n", ret);
-				goto out;
+
+				/*
+				 * Do not treat the transient failure of the
+				 * Jitter RNG as an error that needs to be
+				 * reported. The combined number of the
+				 * maximum reseed threshold times the maximum
+				 * number of Jitter RNG transient errors is
+				 * less than the reseed threshold required by
+				 * SP800-90A allowing us to treat the
+				 * transient errors as such.
+				 *
+				 * However, we mandate that at least the first
+				 * seeding operation must succeed with the
+				 * Jitter RNG.
+				 */
+				if (!reseed || ret != -EAGAIN)
+					goto out;
 			}
 
 			drbg_string_fill(&data1, entropy, entropylen * 2);
@@ -1492,6 +1504,8 @@ static int drbg_prepare_hrng(struct drbg_state *drbg)
 	if (list_empty(&drbg->test_data.list))
 		return 0;
 
+	drbg->jent = crypto_alloc_rng("jitterentropy_rng", 0, 0);
+
 	INIT_WORK(&drbg->seed_work, drbg_async_seed);
 
 	drbg->random_ready.owner = THIS_MODULE;
@@ -1512,8 +1526,6 @@ static int drbg_prepare_hrng(struct drbg_state *drbg)
 		return err;
 	}
 
-	drbg->jent = crypto_alloc_rng("jitterentropy_rng", 0, 0);
-
 	/*
 	 * Require frequent reseeds until the seed source is fully
 	 * initialized.
diff --git a/include/crypto/drbg.h b/include/crypto/drbg.h
index 8c9af21efce1..c4165126937e 100644
--- a/include/crypto/drbg.h
+++ b/include/crypto/drbg.h
@@ -184,11 +184,7 @@ static inline size_t drbg_max_addtl(struct drbg_state *drbg)
 static inline size_t drbg_max_requests(struct drbg_state *drbg)
 {
 	/* SP800-90A requires 2**48 maximum requests before reseeding */
-#if (__BITS_PER_LONG == 32)
-	return SIZE_MAX;
-#else
-	return (1UL<<48);
-#endif
+	return (1<<20);
 }
 
 /*
-- 
2.25.2

Re: [PATCH v2 0/2] crypto: Jitter RNG SP800-90B compliance

[Herbert Xu]

On Fri, Apr 17, 2020 at 09:32:53PM +0200, Stephan Müller wrote:
> Hi,
> 
> This patch set adds SP800-90B compliance to the Jitter RNG. The
> SP800-90B patch is tested for more than half a year in user space
> with the Jitter RNG version 2.2.0.
> 
> The full SP800-90B assessment of the Jitter RNG is provided at [1].
> 
> In addition, the DRBG implementation is updated to always be
> reseeded from the Jitter RNG. To ensure the DRBG is reseeded within
> an appropriate amount of time, the reseed threshold is lowered.
> 
> Changes v2:
> * Instead of free/alloc of the Jitter RNG instance in case of a health
>   test error, re-initialize the RNG instance by performing the
>   power-up test and after a success, clear the health test status and
>   error.
> 
> [1] http://www.chronox.de/jent/doc/CPU-Jitter-NPTRNG.pdf
> 
> Stephan Mueller (2):
>   crypto: Jitter RNG SP800-90B compliance
>   crypto: DRBG always seeded with SP800-90B compliant noise source
> 
>  crypto/drbg.c                |  26 ++-
>  crypto/jitterentropy-kcapi.c |  27 +++
>  crypto/jitterentropy.c       | 417 ++++++++++++++++++++++++++---------
>  include/crypto/drbg.h        |   6 +-
>  4 files changed, 363 insertions(+), 113 deletions(-)

All applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt