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Subject[PATCH 4.19 171/234] crypto: drbg - add FIPS 140-2 CTRNG for noise source
Date
From: Stephan Mueller <smueller@chronox.de>

commit db07cd26ac6a418dc2823187958edcfdb415fa83 upstream.

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
e192be9d9a30555aae2ca1dc3aad37cba484cd4a .

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
b3614763059b82c26bdd02ffcb1c016c1132aad0 .

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>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
crypto/drbg.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++++--
include/crypto/drbg.h | 2 +
2 files changed, 93 insertions(+), 3 deletions(-)

--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -220,6 +220,57 @@ static inline unsigned short drbg_sec_st
}

/*
+ * FIPS 140-2 continuous self test for the noise source
+ * The test is performed on the noise source input data. Thus, the function
+ * implicitly knows the size of the buffer to be equal to the security
+ * strength.
+ *
+ * Note, this function disregards the nonce trailing the entropy data during
+ * initial seeding.
+ *
+ * drbg->drbg_mutex must have been taken.
+ *
+ * @drbg DRBG handle
+ * @entropy buffer of seed data to be checked
+ *
+ * return:
+ * 0 on success
+ * -EAGAIN on when the CTRNG is not yet primed
+ * < 0 on error
+ */
+static int drbg_fips_continuous_test(struct drbg_state *drbg,
+ const unsigned char *entropy)
+{
+ unsigned short entropylen = drbg_sec_strength(drbg->core->flags);
+ int ret = 0;
+
+ if (!IS_ENABLED(CONFIG_CRYPTO_FIPS))
+ return 0;
+
+ /* skip test if we test the overall system */
+ if (list_empty(&drbg->test_data.list))
+ return 0;
+ /* only perform test in FIPS mode */
+ if (!fips_enabled)
+ return 0;
+
+ if (!drbg->fips_primed) {
+ /* Priming of FIPS test */
+ memcpy(drbg->prev, entropy, entropylen);
+ drbg->fips_primed = true;
+ /* priming: another round is needed */
+ return -EAGAIN;
+ }
+ ret = memcmp(drbg->prev, entropy, entropylen);
+ if (!ret)
+ panic("DRBG continuous self test failed\n");
+ memcpy(drbg->prev, entropy, entropylen);
+
+ /* the test shall pass when the two values are not equal */
+ return 0;
+}
+
+/*
* Convert an integer into a byte representation of this integer.
* The byte representation is big-endian
*
@@ -998,6 +1049,22 @@ static inline int __drbg_seed(struct drb
return ret;
}

+static inline int drbg_get_random_bytes(struct drbg_state *drbg,
+ unsigned char *entropy,
+ unsigned int entropylen)
+{
+ int ret;
+
+ do {
+ get_random_bytes(entropy, entropylen);
+ ret = drbg_fips_continuous_test(drbg, entropy);
+ if (ret && ret != -EAGAIN)
+ return ret;
+ } while (ret);
+
+ return 0;
+}
+
static void drbg_async_seed(struct work_struct *work)
{
struct drbg_string data;
@@ -1006,16 +1073,20 @@ static void drbg_async_seed(struct work_
seed_work);
unsigned int entropylen = drbg_sec_strength(drbg->core->flags);
unsigned char entropy[32];
+ int ret;

BUG_ON(!entropylen);
BUG_ON(entropylen > sizeof(entropy));
- get_random_bytes(entropy, entropylen);

drbg_string_fill(&data, entropy, entropylen);
list_add_tail(&data.list, &seedlist);

mutex_lock(&drbg->drbg_mutex);

+ ret = drbg_get_random_bytes(drbg, entropy, entropylen);
+ if (ret)
+ goto unlock;
+
/* If nonblocking pool is initialized, deactivate Jitter RNG */
crypto_free_rng(drbg->jent);
drbg->jent = NULL;
@@ -1030,6 +1101,7 @@ static void drbg_async_seed(struct work_
if (drbg->seeded)
drbg->reseed_threshold = drbg_max_requests(drbg);

+unlock:
mutex_unlock(&drbg->drbg_mutex);

memzero_explicit(entropy, entropylen);
@@ -1081,7 +1153,9 @@ static int drbg_seed(struct drbg_state *
BUG_ON((entropylen * 2) > sizeof(entropy));

/* Get seed from in-kernel /dev/urandom */
- get_random_bytes(entropy, entropylen);
+ ret = drbg_get_random_bytes(drbg, entropy, entropylen);
+ if (ret)
+ goto out;

if (!drbg->jent) {
drbg_string_fill(&data1, entropy, entropylen);
@@ -1094,7 +1168,7 @@ static int drbg_seed(struct drbg_state *
entropylen);
if (ret) {
pr_devel("DRBG: jent failed with %d\n", ret);
- return ret;
+ goto out;
}

drbg_string_fill(&data1, entropy, entropylen * 2);
@@ -1121,6 +1195,7 @@ static int drbg_seed(struct drbg_state *

ret = __drbg_seed(drbg, &seedlist, reseed);

+out:
memzero_explicit(entropy, entropylen * 2);

return ret;
@@ -1142,6 +1217,11 @@ static inline void drbg_dealloc_state(st
drbg->reseed_ctr = 0;
drbg->d_ops = NULL;
drbg->core = NULL;
+ if (IS_ENABLED(CONFIG_CRYPTO_FIPS)) {
+ kzfree(drbg->prev);
+ drbg->prev = NULL;
+ drbg->fips_primed = false;
+ }
}

/*
@@ -1211,6 +1291,14 @@ static inline int drbg_alloc_state(struc
drbg->scratchpad = PTR_ALIGN(drbg->scratchpadbuf, ret + 1);
}

+ if (IS_ENABLED(CONFIG_CRYPTO_FIPS)) {
+ drbg->prev = kzalloc(drbg_sec_strength(drbg->core->flags),
+ GFP_KERNEL);
+ if (!drbg->prev)
+ goto fini;
+ drbg->fips_primed = false;
+ }
+
return 0;

fini:
--- a/include/crypto/drbg.h
+++ b/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;

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