From: Alexey Dobriyan <adobriyan@gmail.com>
To: linux-kernel@vger.kernel.org, tytso@mit.edu, kvm@vger.kernel.org
Cc: security@kernel.org
Subject: repeatable boot randomness inside KVM guest
Date: Sat, 14 Apr 2018 22:59:21 +0300 [thread overview]
Message-ID: <20180414195921.GA10437@avx2> (raw)
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.
next reply other threads:[~2018-04-14 19:59 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-14 19:59 Alexey Dobriyan [this message]
2018-04-14 22:41 ` repeatable boot randomness inside KVM guest Andy Lutomirski
2018-04-14 23:09 ` Alexey Dobriyan
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