Re: [PATCH] KVM: arm64: Validate the FF-A memory access descriptor placement

[Sudeep Holla <sudeep.holla@kernel.org>]

On Wed, Apr 22, 2026 at 01:24:02PM +0100, Marc Zyngier wrote:
> On Wed, 22 Apr 2026 11:25:40 +0100,
> Sebastian Ene <sebastianene@google.com> wrote:
> > 
> > Prevent the pKVM hypervisor from making assumptions that the
> > endpoint memory access descriptor (EMAD) comes right after the
> > FF-A memory region header and enforce a strict placement for it
> > when validating an FF-A memory lend/share transaction.
> 
> As I read this, you want to remove a bad assumption...
> 

Indeed, it matches my understanding as well. I got confused with the
code change initially only to realise you want to restrict the choice
of offset.

> > 
> > Prior to FF-A version 1.1 the header of the memory region
> > didn't contain an offset to the endpoint memory access descriptor.
> > The layout of a memory transaction looks like this:
> > 
> >   Field name				| Offset
> > 					 -- 0
> > [ Header (ffa_mem_region)               |__ ep_mem_offset
> >   EMAD 1 (ffa_mem_region_attributes)	|
> > ]
> > 
> > Reject the host from specifying a memory access descriptor offset
> > that is different than the size of the memory region header.
> 
> And yet you decide that you want to enforce this assumption. I don't
> understand how you arrive to this conclusion.
> 
> Looking at the spec, it appears that the offset is *designed* to allow
> a gap between the header and the EMAD. Refusing to handle a it seems to be a
> violation of the spec.
> 

+1

-- 
Regards,
Sudeep