linux-kernel - [PATCH v3 1/1] virtio: rng: add derating factor for use by hwrng core

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Message-Id: <d05dff370dcac5aa2ce4e41a3936543253565d89.1408078439.git.amit.shah@redhat.com>
Date:	Fri, 15 Aug 2014 10:46:36 +0530
From:	Amit Shah <amit.shah@...hat.com>
To:	torvalds@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, hpa@...ux.intel.com,
	Rusty Russell <rusty@...tcorp.com.au>,
	Virtualization List <virtualization@...ts.linux-foundation.org>,
	kvm list <kvm@...r.kernel.org>, jgarzik@...pay.com,
	duwe@....de, Amos Kong <akong@...hat.com>,
	ricardo.neri-calderon@...ux.intel.com, tytso@....edu,
	herbert@...dor.apana.org.au, Amit Shah <amit.shah@...hat.com>
Subject: [PATCH v3 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 or badly-implemented hypervisor is a scenario that's
irrelevant -- such a setup is bound to cause all sorts of badness, and a
compromised hwrng is the least of the user's worries.

Given this, we might as well assume that 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>
Reviewed-by: H. Peter Anvin <hpa@...ux.intel.com>
Reviewed-by: Amos Kong <akong@...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 (hpa)
v3: re-word commit msg (tytso)
---
 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

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