Re: https://firmwaresecurity.com/2018/03/14/sof-project-and-project-acrn/
I am not sure, but I believe that the Project ACRN has a new — or at least revised — security spec, which is a nice read:
https://projectacrn.github.io/latest/developer-guides/hld/hld-security.html
more info:
https://projectacrn.org/
https://github.com/projectacrn/acrn-hypervisor