linux-kernel - Re: [PATCH v2 2/2] virtio: rng: ensure reads happen after successful probe

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Date:	Sun, 6 Jul 2014 23:09:49 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Amit Shah <amit.shah@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Virtualization List <virtualization@...ts.linux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Jason Cooper <jason@...edaemon.net>,
	"# 3.4.x" <stable@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] virtio: rng: ensure reads happen after successful probe

On Sun, Jul 6, 2014 at 10:51 PM, Amit Shah <amit.shah@...hat.com> wrote:
> On (Sun) 06 Jul 2014 [21:38:36], Kees Cook wrote:
>> On Fri, Jul 4, 2014 at 10:34 PM, Amit Shah <amit.shah@...hat.com> wrote:
>> > The hwrng core asks for random data in the hwrng_register() call itself
>> > from commit d9e7972619.  This doesn't play well with virtio -- the
>> > DRIVER_OK bit is only set by virtio core on a successful probe, and
>> > we're not yet out of our probe routine when this call is made.  This
>> > causes the host to not acknowledge any requests we put in the virtqueue,
>> > and the insmod or kernel boot process just waits for data to arrive from
>> > the host, which never happens.
>>
>> Doesn't this mean that virtio-rng won't ever contribute entropy to the system?
>
> The initial randomness?  Yes.  But it'll start contributing entropy as
> soon as it's used as the current source.

How does that happen? I don't see an init function defined for it?

-Kees

-- 
Kees Cook
Chrome OS Security
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