Read APPROTECTSTATUS via firmware

RE: Read APPROTECTSTATUS via firmware

Dmitry — Tue, 16 Jun 2020 14:55:05 GMT

Hi,

you cannot read APPROTECTSTATUS but you can check whether MCU is under debug session, see here. In any case you can make hacker's life harder but cannot stop him from dumping you fw, disassembling it and disabling this check.

RE: Read APPROTECTSTATUS via firmware

Barry — Tue, 16 Jun 2020 14:39:35 GMT

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.

RE: Read APPROTECTSTATUS via firmware

Sigurd — Tue, 16 Jun 2020 14:29:19 GMT

Hi,

[quote user=""]Is it possible to read the value of APPROTECTSTATUS via the firmware?[/quote]

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