On Sat, Oct 02, 2021 at 02:40:55PM -0400, Michael S. Tsirkin wrote:

On Sat, Oct 02, 2021 at 07:20:22AM -0700, Andi Kleen wrote:

quoted

On 10/2/2021 4:14 AM, Greg Kroah-Hartman wrote:

quoted

On Sat, Oct 02, 2021 at 07:04:28AM -0400, Michael S. Tsirkin wrote:

quoted

On Fri, Oct 01, 2021 at 08:49:28AM -0700, Andi Kleen wrote:

quoted

quoted

   Do you have a list of specific drivers and kernel options that you
feel you now "trust"?

For TDX it's currently only virtio net/block/console

But we expect this list to grow slightly over time, but not at a high rate
(so hopefully <10)

Well there are already >10 virtio drivers and I think it's reasonable
that all of these will be used with encrypted guests. The list will
grow.

What is keeping "all" drivers from being on this list?

It would be too much work to harden them all, and it would be pointless
because all these drivers are never legitimately needed in a virtualized
environment which only virtualize a very small number of devices.

quoted

  How exactly are
you determining what should, and should not, be allowed?

Everything that has had reasonable effort at hardening can be added. But if
someone proposes to add a driver that should trigger additional scrutiny in
code review. We should also request them to do some fuzzing.

Looks like out of tree modules get a free pass then.

That's not good.  As we already know if a module is in or out of the
tree, you all should be banning all out-of-tree modules if you care
about these things.  That should be very easy to do if you care.

quoted

How would user space know what drivers have been hardened? This is really
something that the kernel needs to determine. I don't think we can outsource
it to anyone else.

IIUC userspace is the distro. It can also do more than a binary on/off,
e.g. it can decide "only virtio", "no out of tree drivers".
A distro can also ship configs with a specific features
enabled/disabled. E.g. I can see where some GPU drivers will be
included by some distros since they are so useful, and excluded
by others since they are so big and hard to audit.
I don't see how the kernel can reasonably make a stand here.
Is "some audit and some fuzzing" a good policy? How much is enough?

Agreed, that is why the policy for this should be in userspace.

Well if userspace sets the policy then I'm not sure we also want
a kernel one ... but if yes I'd like it to be in a central
place so whoever is building the kernel can tweak it easily
and rebuild, without poking at individual drivers.

And here I thought the requirement was that no one could rebuild their
kernel as it was provided by someone else.

Again, these requirements seem contradicting, but as no one has actually
pointed me at the real list of them, who knows what they are?

thanks,

greg k-h
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