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: <dfce335fefe043868301bacf57120759@intel.com>
Date:   Tue, 25 Aug 2020 17:35:29 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Andy Lutomirski <luto@...nel.org>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>
CC:     Andrew Cooper <andrew.cooper3@...rix.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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)

> > 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.

-Tony