How free actually PBP is ?

[as400]

Every month someone asks this question, but nobody ever worried about microcode.

Do you worry about backdoors? I assume it's veeeeeeeeery difficult to put backdoors in microcode so that 1) a full-fledged OS actually boots to completion while 2) making some programs exploitable by a microcode induced backdoors.

Microcode is just an example. IME is a fact and everyone should be worried.

Some firmware lies in the ROM internal to the SOC. That can't be replaced. Where do you see inflexibility in the current firmware?

I meant something like libreboot/coreboot.