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

[Andi Kleen]

> 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