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

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Date:   Fri, 7 Jan 2022 20:04:36 +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 Fri, Jan 07, 2022 at 08:49:26PM +0300, Kirill A. Shutemov wrote:
> To emulate an instruction the emulator needs two things:
> 
>   - R/W access to the register file to read/modify instruction arguments
>     and see RIP of the faulted instruction.
> 
>   - Read access to memory where instruction is placed to see what to
>     emualte. In this case it is guest kernel text.
> 
> Both of them are not available to VMM in TDX environment:
> 
>   - Register file is never exposed to VMM. When a TD exits to the module,
>     it saves registers into the state-save area allocated for that TD.
>     The module then scrubs these registers before returning execution
>     control to the VMM, to help prevent leakage of TD state.
> 
>   - Memory is encrypted TD-private key. The CPU disallows software other
>     than the TDX module and TDs from making memory accesses using the
>     private key.

Thanks, that's very helpful info. It would be nice to have it in the
commit message.

-- 
Regards/Gruss,
    Boris.

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