LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Steven Rostedt <rostedt@goodmis.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andy Lutomirski <luto@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: WARNING: kernel stack frame pointer has bad value
Date: Wed, 19 Apr 2017 10:12:03 -0400 [thread overview]
Message-ID: <20170419101203.670115bc@gandalf.local.home> (raw)
In-Reply-To: <20170419134457.l7gdyuf4xbe4nns5@treble>
On Wed, 19 Apr 2017 08:44:57 -0500
Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Tue, Apr 18, 2017 at 11:37:14PM -0400, Steven Rostedt wrote:
> > Josh,
> >
> > I'm starting to get a bunch of these warnings, and I'm thinking they
> > are false positives. The stack frame error is recorded at a call from
> > entry_SYSCALL_64_fastpath, where I would expect the bp to not be valid.
> >
> > To trigger this, I only need to go into /sys/kernel/debug/tracing and
> > echo function > current_tracer then cat trace. Maybe function tracer
> > stack frames is messing it up some how, but it always fails at the
> > entry call.
> >
> > Here's the dump;
> >
> > WARNING: kernel stack frame pointer at ffff8800bda0ff30 in sshd:1090 has bad value 000055b32abf1fa8
> ...
> > ffff8800bda0ff20: ffff8800bda0ff30 (0xffff8800bda0ff30)
> > ffff8800bda0ff28: ffffffff810dc945 (SyS_rt_sigprocmask+0x5/0x1a0)
> > ffff8800bda0ff30: 000055b32abf1fa8 (0x55b32abf1fa8)
> > ffff8800bda0ff38: ffffffff81cf502a (entry_SYSCALL_64_fastpath+0x18/0xad)
> > ffff8800bda0ff40: 000055b32abf1fa8 (0x55b32abf1fa8)
> > ffff8800bda0ff48: ffffffff810dc945 (SyS_rt_sigprocmask+0x5/0x1a0)
> > ffff8800bda0ff50: ffffffff81cf502a (entry_SYSCALL_64_fastpath+0x18/0xad)
>
> Thanks for reporting, I hadn't seen this one yet.
>
> The problem is that the unwinder expects the last frame pointer to be at
> a certain address (0xffff8800bda0ff48 in this case), so it can know that
> it reached the end. It's confused by the save_mcount_regs macro, which
> builds some fake frames -- which is good -- but then the last frame is
> at a different offset than what the unwinder expects.
>
> Would it be possible for ftrace to rewrite the stack so that it looks
> like this instead?
>
> > ffff8800bda0ff38: ffff8800bda0ff48 (0xffff8800bda0ff48)
> > ffff8800bda0ff40: ffffffff810dc945 (SyS_rt_sigprocmask+0x5/0x1a0)
> > ffff8800bda0ff48: 000055b32abf1fa8 (0x55b32abf1fa8)
> > ffff8800bda0ff50: ffffffff81cf502a (entry_SYSCALL_64_fastpath+0x18/0xad)
>
> In other words it would overwrite the "SyS_rt_sigprocmask+0x5/0x1a0"
> value on the stack at ffff8800bda0ff48 with the original bp, instead of
> appending to the existing stack. If you would be ok with such an
> approach, I could take a stab at it.
This is because we have to handle each different config differently.
This is the case with FENTRY and FRAME_POINTERS. As I like to keep this
as efficient as possible. To do the above, we need to modify the return
address and then restore it. And handle that for each config type.
>
> The alternative would be to change the unwinder, but I would rather
> avoid having to detect another special case if possible.
I'm not sure what's worse. Modifying all the special cases of ftrace,
or adding a new one to the undwinder.
You can take a crack at it if you like, but it needs to be negligible
in the performance of FENTRY and no frame pointers.
-- Steve
next prev parent reply other threads:[~2017-04-19 14:12 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-19 3:37 Steven Rostedt
2017-04-19 13:44 ` Josh Poimboeuf
2017-04-19 14:12 ` Steven Rostedt [this message]
2017-04-19 16:38 ` Josh Poimboeuf
2018-04-19 15:57 syzbot
2018-04-19 17:28 ` Dmitry Vyukov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170419101203.670115bc@gandalf.local.home \
--to=rostedt@goodmis.org \
--cc=hpa@zytor.com \
--cc=jpoimboe@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mingo@kernel.org \
--cc=tglx@linutronix.de \
--subject='Re: WARNING: kernel stack frame pointer has bad value' \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).