On Tue, Oct 12, 2021 at 02:18:01PM -0700, Andi Kleen wrote:

quoted

Interesting. VT-d tradeoffs ... what are they?

The connection to the device is not encrypted and also not authenticated.

This is different that even talking to the (untrusted) host through shared
memory where you at least still have a common key.

Well it's different sure enough but how is talking to host less secure?
Cold boot attacks and such?

quoted

Allowing hypervisor to write into BIOS looks like it will
trivially lead to code execution, won't it?

This is not about BIOS code executing. While the guest firmware runs it is
protected of course. This is for BIOS structures like ACPI tables that are
mapped by Linux. While AML can run byte code it can normally not write to
arbitrary memory.

I thought you basically create an OperationRegion of SystemMemory type,
and off you go. Maybe the OSPM in Linux is clever and protects
some memory, I wouldn't know.

The risk is more that all the Linux code dealing with this hasn't been
hardened to deal with malicious input.

-Andi

-- 
MST