At the moment we use /dev/random as the backing device to provide random numbers to our virtio-rng implementation. The downside of doing so is that it may block indefinitely - or return EAGAIN repeatedly in our case. On one headless system without ample noise sources (no keyboard, mouse, or network traffic) I measured 30 seconds to gain one byte of randomness. At the moment EDK II insists in waiting for all of the requsted random bytes (for its EFI_RNG_PROTOCOL runtime service) to arrive, that held up a Linux kernel boot for more than 10 minutes(!). According to the Internet(TM), on Linux /dev/urandom provides the same quality random numbers as /dev/random, it just does not block when the entropy estimation algorithm suggests so. For all practical purposes the recommendation is to just use /dev/urandom, QEMU did the switch as well in 2019 [1]. Use /dev/urandom instead of /dev/random when opening the file descriptor providing the randomness source for the virtio/rng implementation. Due to a special behaviour documented on the urandom(4) manpage, a read from /dev/urandom will never block, so we can drop the O_NONBLOCK flag. [1] https://gitlab.com/qemu-project/qemu/-/commit/a2230bd778d8 Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx> Reviewed-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx> --- virtio/rng.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/virtio/rng.c b/virtio/rng.c index 8f85d5ec1..e6e70ced3 100644 --- a/virtio/rng.c +++ b/virtio/rng.c @@ -166,7 +166,7 @@ int virtio_rng__init(struct kvm *kvm) if (rdev == NULL) return -ENOMEM; - rdev->fd = open("/dev/random", O_RDONLY | O_NONBLOCK); + rdev->fd = open("/dev/urandom", O_RDONLY); if (rdev->fd < 0) { r = rdev->fd; goto cleanup; -- 2.25.1
