crypto: drbg - add FIPS 140-2 CTRNG for noise source

FIPS 140-2 section 4.9.2 requires a continuous self test of the noise
source. Up to kernel 4.8 drivers/char/random.c provided this continuous
self test. Afterwards it was moved to a location that is inconsistent
with the FIPS 140-2 requirements. The relevant patch was
e192be9d9a .

Thus, the FIPS 140-2 CTRNG is added to the DRBG when it obtains the
seed. This patch resurrects the function drbg_fips_continous_test that
existed some time ago and applies it to the noise sources. The patch
that removed the drbg_fips_continous_test was
b361476305 .

The Jitter RNG implements its own FIPS 140-2 self test and thus does not
need to be subjected to the test in the DRBG.

The patch contains a tiny fix to ensure proper zeroization in case of an
error during the Jitter RNG data gathering.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Reviewed-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/drbg.h

@@ -129,6 +129,8 @@ struct drbg_state {
 
 	bool seeded;		/* DRBG fully seeded? */
 	bool pr;		/* Prediction resistance enabled? */
+	bool fips_primed;	/* Continuous test primed? */
+	unsigned char *prev;	/* FIPS 140-2 continuous test value */
 	struct work_struct seed_work;	/* asynchronous seeding support */
 	struct crypto_rng *jent;
 	const struct drbg_state_ops *d_ops;