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SubjectRe: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy
On Tue, Aug 09, 2016 at 02:04:44PM +0000, Jason Cooper wrote:
>
> iiuc, Ted, you're saying using the hw_random framework would be
> disasterous because despite most drivers having a default quality of 0,
> rngd assumes 1 bit of entropy for every bit read?

Sorry, what I was trying to say (but failed) was that bypassing the
hwrng framework and injecting entropy directly the entropy pool was
disatrous.

> Thankfully, most hw_random drivers don't set the quality. So unless the
> user sets the default_quality param, it's zero.

The fact that this is "most" and not "all" does scare me a little.

As far as I'm concerned *all* hw_random drivers should set quality to
zero, since it should be up to the system administrator. Perhaps the
one exception is virtio_rng, since if you don't trust the hypvervisor,
the security of the VM is hopeless. That being said, I have seen
configurations of KVM which use:

-object rng-random,filename=/dev/urandom,id=rng0 \
-device virtio-rng-pci,rng=rng0

Which is somewhat non-ideal. (Try running od -x /dev/random on such a
guest system....)

- Ted

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