The management interfaces are backed into the cpu dies these days, and typically have full access to all the same busses as the regular cpu cores do, in addition to being able to reprogram the cpu microcode itself. I’m combining/glossing over the facilities somewhat, bu the point remains that true root access to the cpu’s management interface really is potentially a circuit-breaker level problem.
The management interfaces are backed into the cpu dies these days, and typically have full access to all the same busses as the regular cpu cores do, in addition to being able to reprogram the cpu microcode itself. I’m combining/glossing over the facilities somewhat, bu the point remains that true root access to the cpu’s management interface really is potentially a circuit-breaker level problem.