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

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Date:	Mon, 7 Jul 2014 11:21:07 +0530
From:	Amit Shah <amit.shah@...hat.com>
To:	Kees Cook <keescook@...omium.org>
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) 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.

Is this a huge negative?

		Amit
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