Re: Seeding the Linux RNG at first boot

[Leo Famulari <leo@famulari.name>]

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On Thu, Dec 07, 2017 at 10:07:38PM +0100, Ludovic Courtès wrote:
> Leo Famulari <leo@famulari.name> skribis:
> > On the guest side, we would extend urandom-seed-service to also draw on
> > /dev/hwrng, which is where virtio-rng-pci makes the data from the host
> > available.
> 
> Maybe ‘virtualized-operating-system’ in (gnu system vm) could
> automatically customize ‘rngd-service-type’ (or add it)?

Yes, we could do that, although I don't think it's necessary to run a
daemon continuously. It is enough to seed the RNG once.

At the same time we handle the random seed, we could also try reading
from /dev/hwrng and, if the read is successful, copy some bytes into
/dev/urandom. We'd have to try reading and handle failure since we
always create /dev/hwrng regardless of whether the Linux kernel module
is loaded or not.

> > I have an idea for another improvement: to add an argument like
> > "--entropy-seed=" to `guix system` that could place the value in
> > '/var/lib/random-seed', where it would be used on first boot.
> 
> We could do that, though I very much prefer the idea of a “backdoor” à
> la virtio-rng-pci, because it allows to stick to bit-reproducible images
> (well, they’re not bit-reproducible yet I suppose, but let’s not add to
> it.)

I think it would be most useful for disk images, for which there is no
host.

If one always passes the same value to --entropy-seed, it will not
negatively affect the reproducibility of the image ;)

This would not be something we do for the official release image, but
merely an optional tool.

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