> When the device powers on, the Primary Boot Loader in the processor's ROM loads and verifies the eXtensible Boot Loader (XBL). XBL reads the current anti-rollback version from the Qfprom fuses and compares it against the firmware's embedded version number. If the firmware version is lower than the fuse value, boot is rejected. When newer firmware successfully boots, the bootloader issues commands through Qualcomm's TrustZone to blow additional fuses, permanently recording the new minimum version
What exactly is it comparing? What is the “firmware embedded version number”? With an unlocked bootloader you can flash boot and super (system, vendor, etc) partitions, but I must be missing something because it seems like this would be bypassable.
It does say
> Custom ROMs package firmware components from the stock firmware they were built against. If a user's device has been updated to a fused firmware version & they flash a custom ROM built against older firmware, the anti-rollback mechanism triggers immediately.
and I know custom ROMs will often say “make sure you flash stock version x.y beforehand” to ensure you’re on the right firmware, but I’m not sure what partitions that actually refers to (and it’s not the same as vendor blobs), or how much work it is to either build a custom ROM against a newer firmware or patch the (hundreds of) vendor blobs.
What exactly is it comparing? What is the “firmware embedded version number”? With an unlocked bootloader you can flash boot and super (system, vendor, etc) partitions, but I must be missing something because it seems like this would be bypassable.
It does say
> Custom ROMs package firmware components from the stock firmware they were built against. If a user's device has been updated to a fused firmware version & they flash a custom ROM built against older firmware, the anti-rollback mechanism triggers immediately.
and I know custom ROMs will often say “make sure you flash stock version x.y beforehand” to ensure you’re on the right firmware, but I’m not sure what partitions that actually refers to (and it’s not the same as vendor blobs), or how much work it is to either build a custom ROM against a newer firmware or patch the (hundreds of) vendor blobs.