BUS FAULT when calling SYS_INIT and using secure services

Question

Hi!

I'm running into quite a strange problem which is that when trying to use SPM secure services in my program, I get a BUS FAULT error.

What's also really strange is that the error doesn't occur on the function call but a few ms after. The function exits correctly and returns the expected value and then, the program crashes.

When I try to remove the secure function call, the BUS FAULT error stops occurring as well as when I remove all SYS_INIT. No matter which one I keep, I get the BUS FAULT error.

K_SEM_DEFINE(sem_end, 0, 1)

void main(void)
{
	printk("Calling secure function\n");

	uint32_t result;

	int ret = spm_request_read(&result, (uint32_t)&NRF_FICR_S->INFO.PART,
		sizeof(uint32_t));

	if (ret != 0) {
		printk("Could not read FICR (err: %d)\n", ret);
	}
	printk("FICR.INFO.PART = 0x%08X\n\n", result);

	printk("Calling secure function success!\n");

	k_sem_take(&sem_end, K_FOREVER);
}

LOG output:

Calling secure function
FICR.INFO.PART = 0x00009120

Calling secure function success!
[00:00:01.583,923] <inf> protobuf: Initializing protobuf
[00:00:02.583,953] <err> os: ***** MPU FAULT *****
[00:00:02.583,984] <err> os:   Instruction Access Violation
[00:00:02.583,984] <err> os: r0/a1:  0x00000000  r1/a2:  0xe000ed00  r2/a3:  0x200156c0
[00:00:02.583,984] <err> os: r3/a4:  0x20014a00 r12/ip:  0x871dfabe r14/lr:  0x0001c80d
[00:00:02.584,014] <err> os:  xpsr:  0x61000000
[00:00:02.584,014] <err> os: Faulting instruction address (r15/pc): 0xab55d3c4
[00:00:02.584,014] <err> os: >>> ZEPHYR FATAL ERROR 0: CPU exception on CPU 0
[00:00:02.584,014] <err> os: Current thread: 0x20014a00 (unknown)
[00:00:02.646,697] <err> os: Halting system

There is nothing special happening in that protobuf function except the LOG output (I disabled everything else):

static int protobuf_init(const struct device *dev)
{
	ARG_UNUSED(dev);

	LOG_INF("Initializing protobuf");

	return 0;
}

SYS_INIT(protobuf_init, APPLICATION, CONFIG_APPLICATION_INIT_PRIORITY);

Thanks by advance to anyone that can help me with this issue !

Fares Chati · Answer

Hi H&aring;kon, 
 First of all, thank you for your answer. 
 Before reading your answer, I tried several things and finally tried to update the sdk_nrf and this happened to fix the issue. I know it is not the best kind of fix since I don't know for sure what was causing the issue but looking at the modifications made to SPM, this seems to be related to the FPU driver. Indeed, on the update, the FPU driver is no longer used in favor of the CC3XX driver for RNG (Random Number Generation). 
 Please note that reading the "select FPU" attribute on the SPM subsys Kconfig leads to the FAULT error coming back which is what lead me to think it was related to it. 
 Anyway, thank you again for your help! 
 Kind regards, 
 Far&egrave;s

BUS FAULT when calling SYS_INIT and using secure services

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