[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Thu, 12 Dec 2013 13:40:26 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To: Jiri Kosina <jkosina@...e.cz>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...nel.org>,
Andi Kleen <ak@...ux.intel.com>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
Frederic Weisbecker <fweisbec@...il.com>, x86@...nel.org,
lkml <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Ingo Molnar <mingo@...hat.com>, systemtap@...rceware.org,
"H. Peter Anvin" <hpa@...or.com>,
Sasha Levin <sasha.levin@...cle.com>,
Thomas Gleixner <tglx@...utronix.de>,
Seiji Aguchi <seiji.aguchi@....com>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers
directly from do_int3/do_debug
(2013/12/11 22:31), Jiri Kosina wrote:
> On Tue, 3 Dec 2013, Steven Rostedt wrote:
>
>>> To avoid a kernel crash by probing on lockdep code, call
>>> kprobe_int3_handler and kprobe_debug_handler directly
>>> from do_int3 and do_debug. Since there is a locking code
>>> in notify_die, lockdep code can be invoked. And because
>>> the lockdep involves printk() related things, theoretically,
>>> we need to prohibit probing on much more code...
>>>
>>> Anyway, most of the int3 handlers in the kernel are already
>>> called from do_int3 directly, e.g. ftrace_int3_handler,
>>> poke_int3_handler, kgdb_ll_trap. Actually only
>>> kprobe_exceptions_notify is on the notifier_call_chain.
>>>
>>> So I think this is not a crazy thing.
>>
>> What? Oh, yeah. No, using notifiers in int3 handler is the crazy
>> thing ;-)
>
> Yeah, it's broken. Obviously, if you happen to trigger int3 before the
> notifier has been registered, it'd cause int3 exception to be unhandled.
> See
>
> commit 17f41571bb2c4a398785452ac2718a6c5d77180e
> Author: Jiri Kosina <jkosina@...e.cz>
> Date: Tue Jul 23 10:09:28 2013 +0200
>
> kprobes/x86: Call out into INT3 handler directly instead of using notifier
>
> for one such issue that happened with jump labels.
>
>> Hmm, if there's no users of the int3 notifier, should we just remove it?
>
> Hmm, there are still uprobes, right?
Right, uprobes still use it, however, since it only handles user-space
breakpoint, there is no problem.
Thank you!
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists