Linux Virtualization - Aug 2014 - [PATCH 1/1] virtio: rng: add derating factor for use by hwrng core

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 at redhat.com>

---
Pretty small and contained patch; would be great if it is picked up for
3.17.
---
 drivers/char/hw_random/virtio-rng.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/char/hw_random/virtio-rng.c
b/drivers/char/hw_random/virtio-rng.c
index 0027137..2e3139e 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -116,6 +116,7 @@ static int probe_common(struct virtio_device *vdev)
 		.cleanup = virtio_cleanup,
 		.priv = (unsigned long)vi,
 		.name = vi->name,
+		.quality = 1000,
 	};
 	vdev->priv = vi;
 
-- 
1.9.3

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 at redhat.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

On (Mon) 11 Aug 2014 [15:11:03], H. Peter Anvin wrote:
> 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 at redhat.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.
Yea; I meant ruled out in that sense.  Should the commit msg be more
verbose?

		Amit