linux-kernel - Re: [PATCH v8 06/11] x86/traps: Add #VE support for TDX guest

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Message-ID: <924d36a6-480b-2ef4-4691-dc010ed82d45@linux.intel.com>
Date:   Mon, 11 Oct 2021 09:49:15 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Lai Jiangshan <jiangshanlai+lkml@...il.com>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 06/11] x86/traps: Add #VE support for TDX guest


> Minor clarification: it eliminates the chance of a #VE during the syscall gap
> _if the VMM is benign_.  If the VMM is malicious, it can unmap and remap the
> syscall page to induce an EPT Violation #VE due to the page not being accepted.

This has been addressed. The TDX module will support a mode that forbids 
unmapping pages permanently, and Linux is going to check/enforce that 
this mode is enabled. The patch for the check is not included in the 
posted patches yet though.


>
> This question?
>
>    Can the hypervisor cause an already-accepted secure-EPT page to transition to
>    the unaccepted state?
>
> Yep.  I wrote the above before following the link, I should have guessed which
> question it was :-)
>
> IIRC, the proposed middle ground was to add a TDCALL and/or TDPARAMS setting that
> would allow the guest to opt-out of EPT Violation #VE due to page not accepted,

It's a TDPARAMS setting


-Andi