linux-kernel - Re: [PATCH 1/1] virtio: rng: add derating factor for use by hwrng core

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Date:	Mon, 11 Aug 2014 15:11:03 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Amit Shah <amit.shah@...hat.com>, linux-kernel@...r.kernel.org
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Virtualization List <virtualization@...ts.linux-foundation.org>,
	kvm list <kvm@...r.kernel.org>, jgarzik@...pay.com,
	duwe@....de, Amos Kong <akong@...hat.com>,
	ricardo.neri-calderon@...ux.intel.com, tytso@....edu,
	herbert@...dor.apana.org.au
Subject: Re: [PATCH 1/1] virtio: rng: add derating factor for use by hwrng
 core

On 08/11/2014 11:49 AM, Amit Shah wrote:
> The khwrngd thread is started when a hwrng device of sufficient
> quality is registered.  The virtio-rng device is backed by the
> hypervisor, and we trust the hypervisor to provide real entropy.  A
> malicious hypervisor is a scenario that's ruled out, so we are certain
> the quality of randomness we receive is perfectly trustworthy.  Hence,
> we use 100% for the factor, indicating maximum confidence in the source.
> 
> Signed-off-by: Amit Shah <amit.shah@...hat.com>

It isn't "ruled out", it is just irrelevant: if the hypervisor is
malicious, the quality of your random number source is the least of your
problems.

	-hpa


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