[PATCH 5.4 062/240] random: continually use hwgenerator randomness

Greg Kroah-Hartman
2022-06-20T13:38:09Z

From: Dominik Brodowski <linux@dominikbrodowski.net>

commit c321e907aa4803d562d6e70ebed9444ad082f953 upstream.

The rngd kernel thread may sleep indefinitely if the entropy count is
kept above random_write_wakeup_bits by other entropy sources. To make
best use of multiple sources of randomness, mix entropy from hardware
RNGs into the pool at least once within CRNG_RESEED_INTERVAL.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2195,13 +2195,15 @@ void add_hwgenerator_randomness(const ch
return;
}

- /* Suspend writing if we're above the trickle threshold.
+ /* Throttle writing if we're above the trickle threshold.
* We'll be woken up again once below random_write_wakeup_thresh,
- * or when the calling thread is about to terminate.
+ * when the calling thread is about to terminate, or once
+ * CRNG_RESEED_INTERVAL has lapsed.
*/
- wait_event_interruptible(random_write_wait,
+ wait_event_interruptible_timeout(random_write_wait,
!system_wq || kthread_should_stop() ||
- POOL_ENTROPY_BITS() <= random_write_wakeup_bits);
+ POOL_ENTROPY_BITS() <= random_write_wakeup_bits,
+ CRNG_RESEED_INTERVAL);
mix_pool_bytes(buffer, count);
credit_entropy_bits(entropy);
}