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

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Message-ID: <87ft8ay098.fsf@nanos.tec.linutronix.de>
Date:   Tue, 25 Aug 2020 21:49:07 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Luck\, Tony" <tony.luck@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Christopherson\, Sean J" <sean.j.christopherson@...el.com>
Cc:     Andrew Cooper <andrew.cooper3@...rix.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Pu Wen <puwen@...on.cn>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <alexander.levin@...rosoft.com>,
        Dirk Hohndel <dirkhh@...are.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Tony W Wang-oc <TonyWWang-oc@...oxin.com>,
        "H. Peter Anvin" <hpa@...ux.intel.com>,
        "Mallick\, Asit K" <asit.k.mallick@...el.com>,
        Gordon Tetlow <gordon@...lows.org>,
        David Kaplan <David.Kaplan@....com>
Subject: RE: TDX #VE in SYSCALL gap (was: [RFD] x86: Curing the exception and syscall trainwreck in hardware)

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