Messages in this thread |  | | Date | Sat, 14 Apr 2018 22:59:21 +0300 | From | Alexey Dobriyan <> | Subject | repeatable boot randomness inside KVM guest |
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SLAB allocators got CONFIG_SLAB_FREELIST_RANDOM option which randomizes allocation pattern inside a slab:
#ifdef CONFIG_SLAB_FREELIST_RANDOM /* 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 */ prandom_seed_state(&state, get_random_long());
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.
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