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

Sudeep Holla
2026-04-22T19:17:32Z

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