Read APPROTECTSTATUS via firmware

[Barry]

Is it possible to read the value of  APPROTECTSTATUS via the firmware? It seems like the AP register in not memory mapped, so maybe not. But maybe there is some kind of work around. Thanks.

[Sigurd]

Hi,

Is it possible to read the value of  APPROTECTSTATUS via the firmware?

No.  APPROTECTSTATUS is a register that is only visible to the debugger. It cannot be read by the CPU / firmware.

[Barry]

I guess that is something that is dictated by the hardware. If there was a way for the CPU to read this register, then that seems like it could be part of a software mitigation for this vulnerability, https://infocenter.nordicsemi.com/pdf/in_133_v1.0.pdf

In the exploit described, the attacker read this value after his exploit and it was true to the status. It showed enabled before the exploit, and disabled after the exploit. So in my code if I could read this value, I could compare it to the UICR value for approtect and if there was a mismatch I could chose to do something like restart or erase flash.