[RFC PATCH 23/41] random: don't award entropy to non-SP800-90B arch RNGs in FIPS mode

[Nicolai Stange]

It is required by SP800-90C that only SP800-90B compliant entropy sources
may be used for seeding DRBGs.

Don't award any entropy to arch_get_random_long() if fips_enabled is
true. Don't award any entropy to arch_get_random_seed_long() if
fips_enabled && !arch_has_sp800_90b_random_seed().

This is achieved by making min_crng_reseed_pool_entropy() return the
full minimum seed size if fips_enabled && !arch_has_sp800_90b_random_seed()
is true. This prevents crng_reseed() from attempting to make up for any
lack of entropy in the input_pool by reading from the architectural RNG.

Make crng_reseed() bail out in FIPS mode if the input_pool provides
insufficient entropy and any of the arch_get_random_seed_long()
invocations fails: there's no statement regarding SP900-90B compliance of
arch_get_random_long() and so it can't be used as a backup.

Signed-off-by: Nicolai Stange <nstange@xxxxxxx>
---
 drivers/char/random.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 7712b4464ef5..aaddee4e4ab1 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1195,9 +1195,13 @@ static int min_crng_reseed_pool_entropy(void)
 	 * up to one half of the minimum entropy needed for
 	 * reseeding. That way it won't dominate the entropy
 	 * collected by other means at input_pool.
+	 * If in FIPS mode, restrict this to SP900-90B compliant
+	 * architectural RNGs.
 	 */
-	if (arch_has_random() || arch_has_random_seed())
+	if (arch_has_sp800_90b_random_seed() ||
+	    (!fips_enabled && (arch_has_random() || arch_has_random_seed()))) {
 		return 8;
+	}
 	return 16;
 }
 
@@ -1233,7 +1237,8 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
 	for (i = 0; i < 8; i++) {
 		unsigned long	rv;
 		if (!arch_get_random_seed_long(&rv) &&
-		    !arch_get_random_long(&rv)) {
+		    ((arch_randomness_required && fips_enabled) ||
+		     !arch_get_random_long(&rv))) {
 			if (arch_randomness_required) {
 				/*
 				 * The input_pool failed to provide
-- 
2.26.2