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Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers directly from do_int3/do_debug
- From: Jiri Kosina <jkosina at suse dot cz>
- To: Steven Rostedt <rostedt at goodmis dot org>
- Cc: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, Ingo Molnar <mingo at kernel dot org>, Andi Kleen <ak at linux dot intel dot com>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Sandeepa Prabhu <sandeepa dot prabhu at linaro dot org>, Frederic Weisbecker <fweisbec at gmail dot com>, x86 at kernel dot org, lkml <linux-kernel at vger dot kernel dot org>, Andrew Morton <akpm at linux-foundation dot org>, Ingo Molnar <mingo at redhat dot com>, systemtap at sourceware dot org, "H. Peter Anvin" <hpa at zytor dot com>, Sasha Levin <sasha dot levin at oracle dot com>, Thomas Gleixner <tglx at linutronix dot de>, Seiji Aguchi <seiji dot aguchi at hds dot com>, "David S. Miller" <davem at davemloft dot net>
- Date: Wed, 11 Dec 2013 14:31:33 +0100 (CET)
- Subject: Re: [PATCH -tip v4 6/6] [RFC] kprobes/x86: Call exception handlers directly from do_int3/do_debug
- Authentication-results: sourceware.org; auth=none
- References: <20131204012841 dot 22118 dot 82992 dot stgit at kbuild-fedora dot novalocal> <20131204012856 dot 22118 dot 91079 dot stgit at kbuild-fedora dot novalocal> <20131203213904 dot 5ff1794c at gandalf dot local dot home>
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@suse.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?
--
Jiri Kosina
SUSE Labs