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

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Message-ID: <87tt3wikmh.fsf@oldenburg.str.redhat.com>
Date: Tue, 01 Jul 2025 06:46:14 +0200
From: Florian Weimer <fweimer@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,  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>
Subject: Re: [PATCH v12 02/14] unwind_user: Add frame pointer support

* Linus Torvalds:

> 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.

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