linux-kernel - Re: [WARNING] livepatch/x86: Invalid return address when checking a stack of the schedule stuff

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Date:   Mon, 22 May 2017 09:04:03 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Jiri Slaby <jslaby@...e.cz>, Miroslav Benes <mbenes@...e.cz>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [WARNING] livepatch/x86: Invalid return address when checking a
 stack of the schedule stuff

On Mon, May 22, 2017 at 01:50:36PM +0200, Petr Mladek wrote:
> Hi,
> 
> I have just tried to apply the livepatch-sample module using
> the consistency model in current Linus' tree (4.12-rc2) and
> got the following warning from the stack checker code:
> 
> [   28.580616] livepatch_sample: tainting kernel with TAINT_LIVEPATCH
> [   28.581572] livepatch_sample: module verification failed: signature and/or required key missing - tainting kernel
> [   28.589943] livepatch: enabling patch 'livepatch_sample'
> [   28.592146] livepatch: 'livepatch_sample': patching...
> [   28.592643] ------------[ cut here ]------------
> [   28.593069] WARNING: CPU: 1 PID: 3699 at arch/x86/kernel/stacktrace.c:132 save_stack_trace_tsk_reliable+0x133/0x1a0

Thanks, I was able to recreate it too.  We should really add
livepatch-sample loading to the kernel selftests.

This seems to be caused by:

  ff3f7e2475bb ("x86/entry: Fix the end of the stack for newly forked tasks")

I'm not sure what I was smoking when I made that patch because now it
seems completely wrong.  Need to think about it a little more.

-- 
Josh