linux-kernel - [PATCH] random: mix hwgenerator randomness before sleeping

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Message-Id: <20220503195141.683217-1-Jason@zx2c4.com>
Date:   Tue,  3 May 2022 21:51:41 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: [PATCH] random: mix hwgenerator randomness before sleeping

The add_hwgenerator_randomness() function is called in a loop from a
kthread by the hwgenerator core. It's supposed to sleep when there's
nothing to do, and wake up periodically for more entropy. Right now it
receives entropy, sleeps, and then mixes it in. This commit reverses the
order, so that it always mixes in entropy sooner and sleeps after. This
way the entropy is more fresh.

Cc: Dominik Brodowski <linux@...inikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 drivers/char/random.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 845f610b6611..d4eae4b167b4 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1154,6 +1154,9 @@ void rand_initialize_disk(struct gendisk *disk)
 void add_hwgenerator_randomness(const void *buffer, size_t count,
 				size_t entropy)
 {
+	mix_pool_bytes(buffer, count);
+	credit_entropy_bits(entropy);
+
 	/*
 	 * Throttle writing if we're above the trickle threshold.
 	 * We'll be woken up again once below POOL_MIN_BITS, when
@@ -1164,8 +1167,6 @@ void add_hwgenerator_randomness(const void *buffer, size_t count,
 			!system_wq || kthread_should_stop() ||
 			input_pool.entropy_count < POOL_MIN_BITS,
 			CRNG_RESEED_INTERVAL);
-	mix_pool_bytes(buffer, count);
-	credit_entropy_bits(entropy);
 }
 EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
 
-- 
2.35.1