Nitro does measure firmware. If any firmware is unexpected, server will essentially stop being connected to the EC2 substrate network and/or server wiped clean automatically. People will be paged automatically, security will likely be pulled in, etc.

There is no reason to measure hypervisor firmware as it’s not firmware in the case of EC2. The BIOS/UEFI firmware on the mobo is overwritten if it’s tampered with. Hypervisor code (always signed, like all code) is streamed via a verifiably secure system on the server (Nitro cards, which make use of measured boot and/or secure boot).

No idea what the customer facing term “Nitro enclaves” means, but EC2 engineers are literally mobilized like an army with pages when any security risk (even minor ones) is determined. Basic stuff like this is covered. We even go as far as guaranteeing core dumps don’t contain any real customer data, even encrypted