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

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Date:	Thu, 10 Jul 2014 14:22:15 +0530
From:	Amit Shah <amit.shah@...hat.com>
To:	Jason Cooper <jason@...edaemon.net>
Cc:	linux-kernel@...r.kernel.org,
	Virtualization List <virtualization@...ts.linux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	herbert@...dor.apana.org.au, keescook@...omium.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] virtio: rng: ensure reads happen after successful
 probe

On (Wed) 09 Jul 2014 [12:18:36], Jason Cooper wrote:
> On Sat, Jul 05, 2014 at 11:04:53AM +0530, Amit Shah 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.
> > 
> > CC: Kees Cook <keescook@...omium.org>
> > CC: Jason Cooper <jason@...edaemon.net>
> > CC: Herbert Xu <herbert@...dor.apana.org.au>
> > CC: <stable@...r.kernel.org> # For v3.15+
> > Signed-off-by: Amit Shah <amit.shah@...hat.com>
> > ---
> >  drivers/char/hw_random/core.c       |  6 ++++++
> >  drivers/char/hw_random/virtio-rng.c | 10 ++++++++++
> >  2 files changed, 16 insertions(+)
> 
> Yeah, I don't think there's any viable way to get random data out of
> virtio-rng at probe time...  :-(
> 
> Reviewed-by: Jason Cooper <jason@...edaemon.net>

Thanks!

		Amit
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