Hubris is a part of booting on our systems in that it executes on both our root of trust and on our service processor -- but both of these execute long before the host CPU. To understand how we boot our host CPU (AMD Milan) on an Oxide compute sled, see my OSFC 2022 talk[0][1], as well as the episode of our Oxide and Friends podcast on holistic boot.[2]
[0] https://speakerdeck.com/bcantrill/i-have-come-to-bury-the-bi...
[1] https://www.osfc.io/2022/talks/i-have-come-to-bury-the-bios-...
[2] https://share.transistor.fm/s/24beb248