casaroli opened a new pull request, #20384:
URL: https://github.com/apache/nuttx/pull/20384
## Summary
In a protected build a module loaded by `exec()` runs as a user task, and
the ELF loader puts it in the text and data heaps (`CONFIG_ARCH_USE_TEXT_HEAP`,
`CONFIG_ARCH_USE_DATA_HEAP`), which on MPS are SRAM2. Nothing gave user code
access to SRAM2: the only grant, in `arm_addregion()`, exists only with
`CONFIG_MM_REGIONS > 1`, and it uses `mpu_user_intsram()`, which on ARMv8-M is
execute-never. So on `mps3-an547:knsh` every module faulted on its first
instruction.
This maps SRAM2 for user code to read, write and execute when either heap is
in use. Privileged execution stays allowed, because a kernel module loaded
with `insmod` lands in the same heaps. The first commit is whitespace only: it
fixes one older nxstyle error in the file.
## Impact
Only a protected MPS build with `CONFIG_ARCH_USE_TEXT_HEAP` or
`CONFIG_ARCH_USE_DATA_HEAP` changes. Today that can only be `mps3-an547`.
SRAM2 becomes writable and executable from user mode. A kernel module
loaded into it is therefore not protected from user code, which is the price of
one heap serving both.
## Testing
`mps3-an547:knsh` under QEMU with `CONFIG_ELF`, both heaps and the ROMFS
variant of `examples/elf`. (That variant is gated on `BUILD_FLAT` in apps, and
the gate was lifted locally for the test.)
```
before: * Executing errno
arm_memfault: Instruction access violation
Assertion failed ... task: errno process: errno 0x21000001
after: * Executing errno, hello, signal, struct, hello++1, hello++2,
hello++3, mutex, pthread, task
Memory Usage End-of-Test:
```
`tools/checkpatch.sh -c -u -m -g` passes.
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