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.
Just like 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 be used to sabotage any program or computation, making BadBIOS (uses radio, not sound) vastly nastier than StuxNet.
American military made a grave mistake by giving access to 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.
