Pretty much anything "evil" that can be done with the Intel Management Engine stuff can be done in SM mode, which was introduced in the 386SL and in every x86 s

Pretty much anything "evil" that can be done with the Intel Management Engine stuff can be done in SM mode, which was introduced in the 386SL and in every x86 since. And that's before we get into update-able microcode, or even asserting that the chip actually matches the RTL if you had access to that. If the supply chain is compromised and you can't trust them, they never needed any new hardware blocks to do bad things. I don't get why people are so obsessed with these new blocks - the level of required trust hasn't really increased.