Title gives my conclusion from empirical events I witnessed and inside info. PSP runs on the same circuit, but isn't the backdoor per se, which has been around for much longer.
The same way AMD was able to change the crypto algorithms for the Zen chip they licensed to China, they can change how the CPU behaves at any system, even those already deployed. This can also be used to sabotage any program or computation, making BadBIOS vastly nastier than Stuxnet.
American military made a grave mistake to partner with the morons of the Brazilian military, who are letting knowledge of this spread like a fire (and misusing it for petty profit and inside jobs to justify a police state). Israel, UK and France also have access, but are much more professional.