linux-kernel - Re: [PATCH 1/2] rngd: add udev rule to source from hwrng if virtio-rng present

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Date:	Mon, 11 Aug 2014 09:50:20 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Torsten Duwe <duwe@....de>, Amit Shah <amit.shah@...hat.com>
CC:	jgarzik@...pay.com,
	Virtualization List <virtualization@...ts.linux-foundation.org>,
	Amos Kong <akong@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org,
	Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH 1/2] rngd: add udev rule to source from hwrng if virtio-rng
 present

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

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