[vbox-dev] virtio-rng et al

Frank Mehnert frank.mehnert at oracle.com
Wed Mar 4 07:55:58 UTC 2015


On Tuesday 03 March 2015 20:31:06 Johannes Ernst wrote:
> What’s the best source of randomness for a Linux guest?
> I’ve been reading about virtio-rng [1]. Can it be made to work with
> VirtualBox?

VirtualBox does not support virtio-rng but I guess it's not very
difficult to add this feature. I'm more worried about support for
hosts/guests different than Linux.

The source for entropy in a virtual machine is in principle the
same like on bare metal, for instance device interrupts and their
distribution over time, several clocks and the time stamp counter.
VirtualBox tries very hard (and this will be even improved in the
next major release) to provide the guest sensible values when
reading the time stamp counter using the RDTSC machine instruction.

But I admit that the sources for entropy within a virtual machine
are limited in comparison to bare metal, mainly because a guest
is usually configured to have only access to virtual devices being
essential for doing it's job.

Dr.-Ing. Frank Mehnert | Software Development Director, VirtualBox
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