crypto: jitter - SP800-90B compliance

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>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

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;