linux-kernel - Re: [PATCH 08/26] x86/tdx: Handle in-kernel MMIO

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Message-ID: <YdhEQTnm+XMxoDPW@zn.tnic>
Date:   Fri, 7 Jan 2022 14:46:41 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/26] x86/tdx: Handle in-kernel MMIO

On Wed, Jan 05, 2022 at 06:43:11PM +0300, Kirill A. Shutemov wrote:
> Not encrypted, saved/restored by TDX module. But yes, cannot be exposed
> (without guest intend).
> 
> I talk here about *why* the traditional way to handle MMIO -- on VMM side
> -- doesn't work for TDX. It's not safe with untrusted VMM.

Lemme see if I understand this correctly: TDX module saves/restores
guest registers so a malicious hypervisor cannot access them? And that's
why you can't do the traditional way MMIO is done?

> readX()/writeX() helpers limit the range of instructions which can trigger
> MMIO. It makes MMIO instruction emulation feasible. Raw access to MMIO
> region allows compiler to generate whatever instruction it wants.
> Supporting all possible instructions is a task of a different scope.

Yap, please add that to the commit message.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette