Hard fault in STM32H7 protected mode

Configuration: `stm32h747i-disco:nsh`. The system hard-faults on boot, and I haven't been able to track down the cause. It seems to occur after a supervisor call for a `boardctl` but I can't see any obvious reason why. I suspect stack corruption but can't tell where it is happening. My `.config` is below, that should be enough to reproduce, I have no extra applications or code in this build.

[My .config and the stack dump is here](https://gist.github.com/hexaglow/cb085ab2b1fe55e2ca02035bbe98e57a)