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

[Steven Rostedt]

On Mon, 30 Jun 2025 19:10:09 -0700
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Mon, 30 Jun 2025 at 17:54, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> >
> > +       /* stack going in wrong direction? */
> > +       if (cfa <= state->sp)
> > +               goto done;  
> 
> I suspect this should do a lot more testing.

Sure.

> 
> > +       /* 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.

Makes sense.

> 
> Maybe even check that it's the same vma?

Hmm, I call on to Jens Remus and ask if s390 can do anything whacky here?
Where something that isn't allowed on other architectures may be allowed
there? I know s390 has some strange type of stack usage.

-- Steve