Linux Virtualization - Aug 2014 - [PATCH 1/2] rngd: add udev rule to source from hwrng if virtio-rng present

On Mon, Aug 11, 2014 at 12:45:27PM +0530, Amit Shah
wrote:
> 
> What's the suggested value for rng->quality, though, for virtio-rng
> that I can use to ensure the kthread starts?
> 
> Should I use the 700 (70%) as proposed in the original patchset?  I'm
> not exactly sure how that value will be used as well..
There is no such thing as a suggested value, every number is wrong
to some degree.  The quality is an estimation of how random your
source really is; it's a property of your hardware. If the device is
virtual you're in trouble ;-)

Either you have a way to query the underlying real hardware, or
you do your whitening and entropy estimation in the backend driver --
then you can claim 100%.

	Torsten

On 08/11/2014 06:30 AM, Torsten Duwe wrote:
> On Mon, Aug 11, 2014 at 12:45:27PM +0530, Amit Shah wrote:
>>
>> What's the suggested value for rng->quality, though, for
virtio-rng
>> that I can use to ensure the kthread starts?
>>
>> Should I use the 700 (70%) as proposed in the original patchset? 
I'm
>> not exactly sure how that value will be used as well..
> 
> There is no such thing as a suggested value, every number is wrong
> to some degree.  The quality is an estimation of how random your
> source really is; it's a property of your hardware. If the device is
> virtual you're in trouble ;-)
> 
> Either you have a way to query the underlying real hardware, or
> you do your whitening and entropy estimation in the backend driver --
> then you can claim 100%.
> 
virtio-rng I feel we could rank at 100%; it is supposed to feed
/dev/random-quality randomness from the VMM.  If the VMM is hostile you
have already lost anyway.

	-hpa