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: <31ff691d-ac71-861d-07f4-113fe3c918aa@intel.com>
Date:   Tue, 25 Aug 2020 11:38:31 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Andrew Cooper <amc96@....ac.uk>,
        "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>,
        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)

On 8/25/20 10:59 AM, Andrew Cooper wrote:
> If I've read the TDX spec/whitepaper properly, the main hypervisor can
> write to all the encrypted pages.  This will destroy data, break the
> MAC, and yields #PF inside the SEAM hypervisor, or the TD when the cache
> line is next referenced.

I think you're talking about:

> Attempting to access a private KeyID by software outside the SEAM
> mode would cause a page-fault exception (#PF).

I don't think that ever results in a TD guest #PF.  "A MAC-verification
failure would be fatal to the TD and lead to its termination."  In this
context, I think that means that the TD stops running and can not be
reentered.