repeatable boot randomness inside KVM guest
- Date: Sat, 14 Apr 2018 22:59:21 +0300
- From: Alexey Dobriyan <adobriyan@xxxxxxxxx>
- Subject: repeatable boot randomness inside KVM guest
SLAB allocators got CONFIG_SLAB_FREELIST_RANDOM option which randomizes
allocation pattern inside a slab:
/* Pre-initialize the random sequence cache */
static int init_cache_random_seq(struct kmem_cache *s)
Then I printed actual random sequences for each kmem cache.
Turned out they were all the same for most of the caches and
they didn't vary across guest reboots.
int cache_random_seq_create(struct kmem_cache *cachep, unsigned int count, gfp_t gfp)
/* Get best entropy at this stage of boot */
Then I searched internet and turned out KVM can pass randomness via
virtio-rng or something. So I linked /dev/urandom.
And it didn't help!
The only way to get randomness for SLAB is to enable RDRAND inside guest.
Is it KVM bug?
For the record I'm using qemu 2.11.1-r2 and whatever F27 ships now.