linux-kernel - Re: [PATCH v3 01/15] stacktrace/x86: add function for detecting reliable stack traces

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Message-ID: <20161220212136.gdy4zof4qlvi6vhi@treble>
Date:   Tue, 20 Dec 2016 15:21:36 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Miroslav Benes <mbenes@...e.cz>, Jessica Yu <jeyu@...hat.com>,
        Jiri Kosina <jikos@...nel.org>, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Heiko Carstens <heiko.carstens@...ibm.com>, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        Vojtech Pavlik <vojtech@...e.com>, Jiri Slaby <jslaby@...e.cz>,
        Chris J Arges <chris.j.arges@...onical.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3 01/15] stacktrace/x86: add function for detecting
 reliable stack traces

On Tue, Dec 20, 2016 at 10:39:16AM +0100, Petr Mladek wrote:
> On Mon 2016-12-19 11:25:49, Josh Poimboeuf wrote:
> > 3) probably some kind of runtime NMI stack checking feature to
> >    complement objtool, along with a lot of burn time to ensure there are
> >    no issues, particularly in entry code
> 
> Could you please provide more details about this NMI stack checking?
> What is it supposed to protect that objtool could not?
> Will it run regularly or will it be just a random check?

save_stack_trace_tsk_reliable(current) would be called periodically from
an NMI handler, and a warning would be printed if it ever doesn't reach
the "end" of the stack (i.e., user-mode pt_regs).  Due to the
performance impact it would probably only be a debug option.

It would verify the special hand-coded areas which objtool isn't smart
enough to understand, like entry code, ftrace, kprobes, bpf.  It would
also make sure that objtool itself didn't missing anything.

-- 
Josh