linux-kernel - [PATCH] random: fix CRNG initialization when random.trust

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Date:   Tue, 19 Mar 2019 13:28:47 -0400
From:   Jon DeVree <nuxi@...lt24.org>
To:     linux-kernel@...r.kernel.org
Cc:     tytso@....edu, Jason@...c4.com, Jon DeVree <nuxi@...lt24.org>
Subject: [PATCH] random: fix CRNG initialization when random.trust_cpu=1

When the system boots with random.trust_cpu=1 it doesn't initialize the
per-NUMA CRNGs because it skips the rest of the CRNG startup code. This
means that the code from 1e7f583af67b ("random: make /dev/urandom scalable
for silly userspace programs") is not used when random.trust_cpu=1.

crash> dmesg | grep random:
[    0.000000] random: get_random_bytes called from start_kernel+0x94/0x530 with crng_init=0
[    0.314029] random: crng done (trusting CPU's manufacturer)
crash> print crng_node_pool
$6 = (struct crng_state **) 0x0

After adding the missing call to numa_crng_init() the per-NUMA CRNGs are
initialized again:

crash> dmesg | grep random:
[    0.000000] random: get_random_bytes called from start_kernel+0x94/0x530 with crng_init=0
[    0.314031] random: crng done (trusting CPU's manufacturer)
crash> print crng_node_pool
$1 = (struct crng_state **) 0xffff9a915f4014a0

The call to invalidate_batched_entropy() was also missing. This is
important for architectures like PPC and S390 which only have the
arch_get_random_seed_* functions.

Fixes: 39a8883a2b98 ("random: add a config option to trust the CPU's hwrng")
Signed-off-by: Jon DeVree <nuxi@...lt24.org>
---
 drivers/char/random.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 38c6d1af6d1c..d4d45ccfeefc 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -777,6 +777,7 @@ static struct crng_state **crng_node_pool __read_mostly;
 #endif
 
 static void invalidate_batched_entropy(void);
+static void numa_crng_init(void);
 
 static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
 static int __init parse_trust_cpu(char *arg)
@@ -805,7 +806,9 @@ static void crng_initialize(struct crng_state *crng)
 		}
 		crng->state[i] ^= rv;
 	}
-	if (trust_cpu && arch_init) {
+	if (trust_cpu && arch_init && crng == &primary_crng) {
+		invalidate_batched_entropy();
+		numa_crng_init();
 		crng_init = 2;
 		pr_notice("random: crng done (trusting CPU's manufacturer)\n");
 	}
-- 
2.20.1