Crash in secure fault handler when spm logging is enabled

[ante]

Hi,

I was tracking down a bug that resulted in a secure fault exception. To save some time tracking it down I enabled logging in the spm. However this resulted in an escalated exception in the spm fault handler. As far as I can see the MCU is in non-secure state when the fault handler in the spm is about to print out the original secure fault exception, this results in an elevated hard fault:

The BFAR address 0x50015504 indicates that the problem is accessing the RTC1_S. Below I have braked the spm code just before the exception gets elevated. This is just before it is about to get a timestamp for a log printout. If I at this point check access to RTC1_S and RTC1_NS using the debugger I can see that RTC1_NS is accessible but RTC1_S is not. For this reason I think the MCU is still in non-secure mode, and as the MCU is executing in the spm code I assume it always will use the secure version of all the HW (in this case RTC1_S).

We are using the nRF9160 sample spm module. In this module I have only added the following config:

CONFIG_LOG=y

The spm module is built as part of the non-secure application by using the app config:

CONFIG_SPM=y

It should be fairly easy to reproduce the issue by in the non-secure application accessing something that is in the secure area, such as:

volatile uint32_t dummy = *((uint32_t *) 0x5000F000);

We are basing our code on the v1.2.0 tag.

[loumay]

Hi Didrik,
Is there news on this topic?

I would be interested to understand why the secure firmware (e.g SPM) can't access a peripheral configured as non-secure.

I only have one UART (configured as NS and used by the NS application) in my setup and it would be useful to print the fault info with it.

Would it be feasible to change the security attribute in the fault back to secure?

[Didrik Rokhaug]

Hi loumay,

There is an open PR that will let you dump non-secure logs from secure faults: https://github.com/nrfconnect/sdk-nrf/pull/3933

[loumay]

Awesome! Thanks for the quick response.