Downgrading Firmware

Firmware Revert

By dumping with hardware Syscon memory and flash memory of a specific PS4 console, one can update the System Software of this PS4 to any version then whenever he wants, restore the dumps in order to restore the older firmware. Then it is required to either restore a HDD dump from that Firmware or to reinstall Firmware with PUP.

Actual Downgrade

There may be a way to downgrade the firmware without need of a hardware backup. This downgrade might be infeasible due to per-console keys and unknown crypto keys used to decrypt PUP and re-encrypt respective flash components. That would require full code execution inside SAMU, or at least keys from SAMU.