The (compromised) Linux decides whether to load the “compromised mode” code or the mp1 secure system? Sounds like an avenue to explore. It says the bootloader itself is secure, but that doesn’t mean much if it’s being loaded into a compromised environment, depending on where it is actually being executed. I guess the coprocessor could be considered a Secure Enclave of Sorts, but the fact that Linux could load a separate bootloader and run that (somehow) is of concern.