Re: [Qemu-devel] [RFC PATCH v1 10/22] sev: add SEV debug decrypt command

[Paolo Bonzini]

On 14/09/2016 17:02, Michael S. Tsirkin wrote:
> If you believe there are attackers that have access to the
> monitor and nothing else, then a feature to disable debugging
> is a generally useful one. But once we merge sev patchset then of course
> sev people disappear and it will be up to others to make it
> work on non-amd CPUs.
> 
> Another is to help merge other parts faster.  E.g.  looking at what
> Daniel writes, the feature might have been over-sold so people will
> disable debugging thinking this will prevent all active attacks. Thus we
> now need to add good documentation so people know what they can actually
> expect to get from QEMU in return for disabling debugging. Why not merge
> the simple "encrypt memory part" while this documentation work is going
> on?

Encrypting memory makes no sense if anyone can ask to decrypt it.  And
I'm not even sure how force-enabling debug r/w, which is literally a
single bit set in the feature register, would make the patchset simpler.

If anything, as I said already, it would make the patchset simpler to
force-*disable* it, since you don't need to introduce debug hooks that
go through the secure processor.

Paolo