Re: TDX #VE in SYSCALL gap (was: [RFD] x86: Curing the exception and syscall trainwreck in hardware)

[Andy Lutomirski]

On Tue, Aug 25, 2020 at 10:36 AM Luck, Tony <tony.luck@xxxxxxxxx> wrote:
>
> > > Or malicious hypervisor action, and that's a problem.
> > >
> > > Suppose the hypervisor remaps a GPA used in the SYSCALL gap (e.g. the
> > > actual SYSCALL text or the first memory it accesses -- I don't have a
> > > TDX spec so I don't know the details).
>
> Is it feasible to defend against a malicious (or buggy) hypervisor?
>
> Obviously, we can't leave holes that guests can exploit. But the hypervisor
> can crash the system no matter how clever TDX is.

Crashing the system is one thing.  Corrupting the system in a way that
could allow code execution is another thing entirely.  And the whole
point of TDX is to defend the guest against the hypervisor.