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

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Message-ID: <CAHk-=wiWOYB4c3E-Cc=D89j0txbN4AGqm0j1dojqHq3uzJ+LqQ@mail.gmail.com>
Date: Mon, 30 Jun 2025 19:10:09 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	bpf@...r.kernel.org, x86@...nel.org, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>, 
	Namhyung Kim <namhyung@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Andrii Nakryiko <andrii@...nel.org>, Indu Bhagat <indu.bhagat@...cle.com>, 
	"Jose E. Marchesi" <jemarch@....org>, Beau Belgrave <beaub@...ux.microsoft.com>, 
	Jens Remus <jremus@...ux.ibm.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Jens Axboe <axboe@...nel.dk>, Florian Weimer <fweimer@...hat.com>
Subject: Re: [PATCH v12 02/14] unwind_user: Add frame pointer support

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

Maybe even check that it's the same vma?

             Linus