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

[Thomas Gleixner]

On Tue, Aug 25 2020 at 17:35, Tony Luck 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.

If it crashes and burns reliably then fine, but is that guaranteed?

I have serious doubts about that given the history and fragility of all
of this and I really have zero interest in dealing with the fallout a
year from now.

Thanks,

        tglx