Re: [PATCH v5 02/22] cc_platform: Add new attribute to prevent ACPI CPU hotplug

[Kai Huang]

On Wed, 2022-08-03 at 11:40 +0800, Binbin Wu wrote:
> host kernel is also not in TDX's TCB either, what would happen if kernel 
> doesn't
> do anything in case of buggy BIOS? How does TDX handle the case to 
> enforce the
> secure of TDs?

TDX doesn't support hot-add or hot-removal CPU from TDX' security perimeter at
runtime.  Even BIOS/kernel can ever bring up new CPUs at runtime, the new CPUs
cannot run within TDX's security domain, in which case TDX's security isn't
compromised.  If kernel schedules a TD to a new added CPU, then AFAICT the
behaviour is TDX module implementation specific but not architectural.  A
reasonable behaviour would be the TDENTER should refuse to run when the CPU
isn't verified by TDX during boot.

If any CPU is hot-removed, then the security's TDX isn't compromised, but TDX is
not guaranteed to functionally work anymore.

-- 
Thanks,
-Kai