# Re: \[PATCH v12 02/14\] unwind\_user: Add frame pointer support

- From: Linus Torvalds \<torvalds@linux-foundation.org\>
- Date: 2025-07-01 02:10:30 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2025/07/3114863
- Thread: https://ratatoskr.run/linux-trace-kernel/2025/07/3114813/t.md

```text
On Mon, 30 Jun 2025 at 17:54, Steven Rostedt [ref] wrote:
>
> +       /* stack going in wrong direction? */
> +       if (cfa <= state->sp)
> +               goto done;

I suspect this should do a lot more testing.

> +       /* Find the Return Address (RA) */
> +       if (get_user(ra, (unsigned long *)(cfa + frame->ra_off)))
> +               goto done;
> +
> +       if (frame->fp_off && get_user(fp, (unsigned long __user *)(cfa + frame->fp_off)))
> +               goto done;

.. and this should check the frame for validity too.  At a minimum it
should be properly aligned, but things like "it had better be above
the current frame" to avoid having some loop would seem to be a good
idea.

Maybe even check that it's the same vma?

             Linus
```