block: disable entropy contributions for nonrot devices

Clear QUEUE_FLAG_ADD_RANDOM in all block drivers that set
QUEUE_FLAG_NONROT.

Historically, all block devices have automatically made entropy
contributions.  But as previously stated in commit e2e1a148 ("block: add
sysfs knob for turning off disk entropy contributions"):
    - On SSD disks, the completion times aren't as random as they
      are for rotational drives. So it's questionable whether they
      should contribute to the random pool in the first place.
    - Calling add_disk_randomness() has a lot of overhead.

There are more reliable sources for randomness than non-rotational block
devices.  From a security perspective it is better to err on the side of
caution than to allow entropy contributions from unreliable "random"
sources.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/block/skd_main.c b/drivers/block/skd_main.c
index 8fcdcfb4b472..1e46eb2305c0 100644
--- a/drivers/block/skd_main.c
+++ b/drivers/block/skd_main.c
@@ -4426,6 +4426,7 @@ static int skd_cons_disk(struct skd_device *skdev)
 	q->limits.discard_zeroes_data = 1;
 	queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, q);
 	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);
+	queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, q);
 
 	spin_lock_irqsave(&skdev->lock, flags);
 	pr_debug("%s:%s:%d stopping %s queue\n",