There are plenty interesting things you could do in processor firmware. Here are three examples:
Tamper with AES and randomness instructions.
Plant a very obscure privilege escalation exploit. Given the prevalence of java, activex and google nacl, escaping sandboxes is a big thing.
Tamper with the MMU to make a certain software invisible.
If they had the opportunity, it's not unlikely they did something like this. Perhaps just in a directed attack. They've done extensive firmware patching in the past in you believe last year's leaks.
A more interesting question is whether they didn't have to, because they had a say in making the silicon in the first place. The risk is there, it's not crazy to see it. Even FreeBSD who was the last mainstream OS to use the randomness instructions unadultered doesn't do that anymore.
Tamper with AES and randomness instructions.
Plant a very obscure privilege escalation exploit. Given the prevalence of java, activex and google nacl, escaping sandboxes is a big thing.
Tamper with the MMU to make a certain software invisible.
If they had the opportunity, it's not unlikely they did something like this. Perhaps just in a directed attack. They've done extensive firmware patching in the past in you believe last year's leaks.
A more interesting question is whether they didn't have to, because they had a say in making the silicon in the first place. The risk is there, it's not crazy to see it. Even FreeBSD who was the last mainstream OS to use the randomness instructions unadultered doesn't do that anymore.