linux-kernel - Re: WARNING: kernel stack frame pointer at ffffffff82e03f40 in swapper:0 has bad value (null)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 12 Dec 2016 15:16:27 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: WARNING: kernel stack frame pointer at ffffffff82e03f40 in
 swapper:0 has bad value           (null)

On Mon, Dec 12, 2016 at 12:10:25PM -0600, Josh Poimboeuf wrote:
> On Mon, Dec 12, 2016 at 06:50:23PM +0100, Borislav Petkov wrote:
> > [    0.000000] ffffffffbce03f40: 0000000000000000 ...
> > [    0.000000] ffffffffbce03f48: ffffffffbc0001b5 (start_cpu+0x5/0x14)
> > [    0.000000] ffffffffbce03f50: ffffffffbc0001b5 (start_cpu+0x5/0x14)
> > [    0.000000] ffffffffbce03f58: 0000000000000000 ...
> > [    0.000000] Linux version 4.9.0-rc8+ (root@...dor) (gcc version 6.2.0 20161109 (Debian 6.2.0-13) ) #2 SMP PREEMPT Mon Dec 12 18:36:48 CET 2016
> 
> Something funky is going on in the head code.  It looks like start_cpu
> is getting executed twice somehow.  Need to do some more head
> scratching...

I still can't figure out what could cause this, nor can I recreate it.

Andy, any idea?  I'm trying to figure out why a stack trace of the
initial task, early in start_kernel(), would show start_cpu() on the
stack *twice*.  The start_cpu() entry on the stack at ffffffffbce03f50
is right where it's supposed to be.  But then there's another
start_cpu() entry at 0xffffffffbce03f48 which is pointed to by the frame
pointer chain.  I can't figure out where that one came from and why the
stack is offset by a word, compared to all the other idle task stacks
I've seen.

Boris, what kind of CPU is it?

-- 
Josh