STM32L5 secure access to non-secure flash block read as zero. Is it an architecturally specified behavior or just an MCU specific behavior?

[WChoi.4]

I am currently experimenting on stm32l562e-dk board, and I discovered that, in the secure world, non-secure flash cannot be read via a secure memory region (i.e. not covered by any of the SAU regions). To be specific, value of zero is read.

I am wondering whether this behavior is architecturally specified or just STM32-specific.

Thanks

[Bubbles]

Hello @WChoi.4​ ,

this is AFAIK intended by ARM architecture and also expected by ARM secure SW such as TFM. If you want the separation to work only one way, you are probably looking for privilege setting, not secure/nonsecure.

BR,

J.