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

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Message-ID: <87zjf88awc.fsf@rustcorp.com.au>
Date:	Thu, 14 Aug 2014 04:39:07 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Linus Torvalds" <torvalds@...ux-foundation.org>
Cc:	hpa@...ux.intel.com, Amos Kong <akong@...hat.com>,
	ricardo.neri-calderon@...ux.intel.com, tytso@....edu,
	Amit Shah <amit.shah@...hat.com>
Subject: [PATCH] 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 irrelevant -- such a setup
is bound to cause all sorts of badness, and a compromised hwrng is not
the biggest threat.

Given this, 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>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
---
Pretty small and contained patch; would be great if it is picked up for
3.17.

v2: re-word commit msg

[Agreed, re-sending to Linus with SOB before jumping on plane]
---
 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;

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