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  • Case ID: 306216
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Zephyr bus fault when using PSA crypto with CC310 and Openthread L2 layer

nealjack

Hello,

I am migrating an application based on the old Nordic SDK16 to the NCS Zephyr SDK.

My workspace is using Zephyr commit f8f11338, nrfconnect/mbedtls commit de1b3f57, and nrfconnect/sdk-nrf commit f06fb7d3.

My application utilizes openthread and also requires the use of ECDSA key management and signing.

To use these features, I use the following configuration options to enable the Openthread L2 layer and the PSA crypto library. These options were adapted from zephyr openthread samples and psa crypto ncs sample configurations.


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# The Zephyr CMSIS emulation assumes that ticks are ms, currently
CONFIG_SYS_CLOCK_TICKS_PER_SEC=1000
CONFIG_MAIN_STACK_SIZE=4096
CONFIG_HEAP_MEM_POOL_SIZE=4096
# Enable loging using RTT and UART
CONFIG_CONSOLE=y
CONFIG_LOG=y
CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_LOG_BACKEND_UART=y
CONFIG_LOG_BUFFER_SIZE=15360
CONFIG_SEGGER_RTT_BUFFER_SIZE_UP=15360
# Enable nordic security backend and PSA APIs
CONFIG_NRF_SECURITY=y
CONFIG_MBEDTLS_PSA_CRYPTO_C=y
# Enable persistent storage APIs
CONFIG_MBEDTLS_PSA_CRYPTO_STORAGE_C=y
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

With this configuration, I find that my application encounters a bus fault during initialization:

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[00:00:00.002,197] <inf> ieee802154_nrf5: nRF5 802154 radio initialized
[00:00:00.002,777] <err> os: ***** BUS FAULT *****
[00:00:00.002,807] <err> os: Imprecise data bus error
[00:00:00.002,807] <err> os: r0/a1: 0x20001700 r1/a2: 0x00000000 r2/a3: 0x200ff8bd
[00:00:00.002,838] <err> os: r3/a4: 0x200ff8bd r12/ip: 0x000001d1 r14/lr: 0x0001a1ad
[00:00:00.002,838] <err> os: xpsr: 0x61000000
[00:00:00.002,868] <err> os: s[ 0]: 0x00000000 s[ 1]: 0x00000000 s[ 2]: 0x00000000 s[ 3]: 0x00000000
[00:00:00.002,868] <err> os: s[ 4]: 0x00000000 s[ 5]: 0x00000000 s[ 6]: 0x00000000 s[ 7]: 0x00000000
[00:00:00.002,899] <err> os: s[ 8]: 0x00000000 s[ 9]: 0x00000000 s[10]: 0x00000000 s[11]: 0x00000000
[00:00:00.002,899] <err> os: s[12]: 0x00000000 s[13]: 0x00000000 s[14]: 0x00000000 s[15]: 0x00000000
[00:00:00.002,929] <err> os: fpscr: 0x2000c734
[00:00:00.002,929] <err> os: Faulting instruction address (r15/pc): 0x00031692
[00:00:00.002,960] <err> os: >>> ZEPHYR FATAL ERROR 0: CPU exception on CPU 0
[00:00:00.002,990] <err> os: Current thread: 0x20006310 (unknown)
[00:00:00.435,333] <err> fatal_error: Resetting system
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Independently, samples that use openthread or PSA features work successfully, including the persistent_key_usage and the ecdsa samples.
I find that enabling the openthread l2 layer in these examples with the config options mentioned above results in the same bus fault that I am experiencing when running my application. I am convinced this is due to a conflict with the usage of the CC310 accelerator between the PSA library and the Openthread stack.

I have tried to use the oberon stack instead of the CC3XX and while the application no longer experiences a bus fault, psa_generate_key always returns (-134). I tracked this down via gdb to key attribute validation in psa_validate_key_attributes(), specifically psa_validate_key_location().

These issues can be replicated with the existing NCS crypto examples and are not unique to my application.


Is there a preferred way to integrate a crypto library and the openthread stack within an NCS Zephyr application that I missed the documentation for? If not, how can I resolve this configuration conflict between openthread and the PSA libraries?

Thanks,
Neal

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