Re: [PATCH v12 02/14] unwind_user: Add frame pointer support

[Florian Weimer <fweimer@redhat.com>]

* Linus Torvalds:

> On Mon, 30 Jun 2025 at 17:54, Steven Rostedt <rostedt@goodmis.org> 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.

I don't think SFrame as-is requires stacks to be contiguous.  Maybe
there could be a per-frame flag that indicates whether a stack switch is
expected?

Thanks,
Florian