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

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

[Rusty Russell]

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@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.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;

Re: [PATCH] virtio: rng: add derating factor for use by hwrng core

[H. Peter Anvin]

On 08/13/2014 12:09 PM, Rusty Russell 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 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@redhat.com>
> Signed-off-by: Rusty Russell <rusty@rustcorp.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]

Reviewed-by: H. Peter Anvin <hpa@linux.intel.com>

Re: [PATCH] virtio: rng: add derating factor for use by hwrng core

[Theodore Ts'o]

On Thu, Aug 14, 2014 at 04:39:07AM +0930, Rusty Russell 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 irrelevant -- such a setup
> is bound to cause all sorts of badness, and a compromised hwrng is not
> the biggest threat.

s/malicious/malicious or badly implemented/

s/is not the biggest threat/is the least of the user's worries/

> 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.

s/we are certain/we might as well assume that/

I won't insist on the wording changes, but I think it's a better way
of phrasing things.

Cheers,

						- Ted

Re: [PATCH] virtio: rng: add derating factor for use by hwrng core

[Amos Kong]

On Thu, Aug 14, 2014 at 04:39:07AM +0930, Rusty Russell 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 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@redhat.com>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>


Reviewed-by: Amos Kong <akong@redhat.com>

> ---
> 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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-- 
			Amos.