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Date: Sat, 16 Apr 2016 04:31:38 -0400 (EDT)
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom
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To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Hubert Kario <hkario@redhat.com>, Eric Blake <eblake@redhat.com>, Cole Robinson <crobinso@redhat.com>, libvirt-list@redhat.com, qemu-devel <qemu-devel@nongnu.org>, "Richard W.M. Jones" <rjones@redhat.com>, "Daniel P. Berrange" <berrange@redhat.com>, Peter Krempa <pkrempa@redhat.com>, Amit Shah <amit.shah@redhat.com>, mik@miknet.net, jjaburek@redhat.com, sgrubb@redhat.com

> Also, I do not believe /dev/urandom is FIPS compliant.  Finally, the refill
> policy is different, so it is not really true the algorithm is the same.
> 
> All in all, other than a seed value it really doesn't make any sense.  Of
> course, none of this matters on newer Intel hardware ;)

Right, but there's always the point about people that use heterogeneous
hosts and cannot pass rdrand/rdseed to the guest.  For these, we should
add a QEMU driver that uses rdrand/rdseed, and thus decouples virtio-rng
from the host /dev/* completely.

>>From the libvirt POV there are various possibilities:

- Libvirt can have a libvirt.conf parameter that says "ignore whatever is
specified in the guest XML if rdrand/rdseed is available, and instead use
rdrand/rdseed".

- Libvirt can allow specifying rdrand/rdseed _and_ an additional backend,
like this:

    <backend model="cpu"/>
    <backend model="random">/dev/random</backend>

and fallback to the second if rdrand/rdseed are not available.

Paolo