nRF53 Non-Secure app Entropy

[mlang3440]

Hi, I am building an application on the nrf5340dk using using nrf5340dk_nrf5340_cpuappns as the target board.

When I have CONFIG_NETWORKING=Y enabled in my prj.conf I am getting this build error:

#error "No cryptocell or cryptocell_sw node labels in the devicetree

From the source file entropy_cc310.c

I realize that the non-secure app has to call the cc312 driver through the SPM services.

However looking in the file spm/Kconfig i found:

config SPM_SERVICE_RNG
    bool "Request random numbers"
    default y if SPM
    select NORDIC_SECURITY_BACKEND if IS_SPM
    select FPU if IS_SPM

# NORDIC_SECURITY_BACKEND is not supported on 53 yet
    depends on ! SOC_NRF5340_CPUAPP

    help
      The Non-Secure Firmware is not allowed to use the crypto hardware.
      This service allows it to request random numbers from the SPM.

Yet it seems that that the SPM_SERVICE_RNG is currently not allowed on the nrf53 for some reason.

Can you better help me understand the issue here, and if there is a workaround. Thanks.

[mlang3440]

I was able to get it to compile by adding

CONFIG_TEST_RANDOM_GENERATOR=y
CONFIG_ENTROPY_CC3XX=n

to the prj.conf.

[Einar Thorsrud]

Hi,

I want to mention that in case it was not clear, using CONFIG_TEST_RANDOM_GENERATOR gives you pseudo random numbers and not true random numbers. So it enables you to develop and test your code, but you cannot use this in production.

There will be support for using the CC312 from non-secure region in the future, but I cannot say exactly when that will be.

[mlang3440]

Yes, I understand its for testing only.

If the CC3XX driver wont even compile on the nrf5340ns then it probably shouldn't automatically be enabled for that target.