Re: [PATCH 0/4] random,x86,kvm: Add and use MSR_KVM_GET_RNG_SEED

Gleb Natapov
2014-07-16T07:23:23Z

On Wed, Jul 16, 2014 at 09:10:27AM +0200, Daniel Borkmann wrote:
> On 07/16/2014 08:41 AM, Gleb Natapov wrote:
> >On Tue, Jul 15, 2014 at 07:48:06PM -0700, Andy Lutomirski wrote:
> >>virtio-rng is both too complicated and insufficient for initial rng
> >>seeding. It's far too complicated to use for KASLR or any other
> >>early boot random number needs. It also provides /dev/random-style
> >>bits, which means that making guest boot wait for virtio-rng is
> >>unacceptably slow, and doing it asynchronously means that
> >>/dev/urandom might be predictable when userspace starts.
> >>
> >>This introduces a very simple synchronous mechanism to get
> >>/dev/urandom-style bits.
> >
> >Why can't you use RDRAND instruction for that?
>
> You mean using it directly? I think simply for the very same reasons
> as in c2557a303a ...
So you trust your hypervisor vendor more than you trust your CPU vendor? :)

--
Gleb.