linux-kernel - Re: [PATCH 2/2] kprobe: fix: Add ftrace_ops_assist

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Message-ID: <20180703183048.1eeeef4a@gandalf.local.home>
Date:   Tue, 3 Jul 2018 18:30:48 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Francis Deslauriers <francis.deslauriers@...icios.com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 2/2] kprobe: fix: Add ftrace_ops_assist_func to kprobe
 blacklist

Mathieu and Francis,

Looking back, this thread never got further. Would Masami's patch work
for you?

-- Steve


On Sat, 17 Mar 2018 10:22:11 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Sat, 17 Mar 2018 09:13:34 +0900
> Masami Hiramatsu <mhiramat@...nel.org> wrote:
> 
> > On Fri, 16 Mar 2018 13:53:01 -0400 (EDT)
> > Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> >   
> > > ----- On Mar 16, 2018, at 12:48 PM, rostedt rostedt@...dmis.org wrote:
> > >   
> > > > On Fri, 16 Mar 2018 12:41:34 -0400
> > > > Steven Rostedt <rostedt@...dmis.org> wrote:
> > > >   
> > > >> Yes, kprobes are dangerous. I'm not saying it shouldn't be fixed, I'm
> > > >> saying that I don't have time to fix it now, but would be happy to
> > > >> accept patches if someone else does so.  
> > > > 
> > > > And looking at what I replied before for the original patch. It would
> > > > probably be a good idea to blacklist directories. Like we do with
> > > > function tracing. We probably should black list both kernel/tracing and
> > > > kernel/events from being probed.
> > > > 
> > > > Did this come up at plumbers? You were there too, I don't remember
> > > > discussing it there.  
> > > 
> > > I don't remember this coming up last Plumbers nor KS neither, given
> > > that we were focused on other topics.
> > > 
> > > Would the general approach you envision be based on emitting all code
> > > generated by compilation of all objects under kernel/tracing and
> > > kernel/events into a specific "nokprobes" text section of the kernel ?
> > > Perhaps we could create a specific linker scripts for those directories,
> > > or do you have in mind a neater way to do this ?  
> > 
> > .kprobes.text section still exists. As I pointed in previous mail, I don't
> > think we have to put all those code into that section. But if you want,
> > it is acceptable to have a kconfig which push most of those ftrace related
> > code into .kprobes.text section.  
> 
> Or, we can check it by ftrace_location_range() as below patch.
> 
> Note that as a side-effect, we can not trace functions in trace_kprobe.c
> anymore, and this means it is hard to me to make a testcase of kprobe events.
> It was the easiest (and maintainable) way to make test cases... sigh.
> 
> -----
> tracing: kprobes: Prohibit probing on notrace function
> 
> From: Masami Hiramatsu <mhiramat@...nel.org>
> 
> Prohibit kprobe-events probing on notrace function.
> Since probing on the notrace function can cause recursive
> event call. In most case those are just skipped, but
> in some case it falls into infinit recursive call.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  kernel/trace/trace_kprobe.c |   23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 5ce9b8cf7be3..7404b012e51a 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -487,6 +487,23 @@ disable_trace_kprobe(struct trace_kprobe *tk, struct trace_event_file *file)
>  	return ret;
>  }
>  
> +#ifdef CONFIG_KPROBES_ON_FTRACE
> +static bool within_notrace_func(struct trace_kprobe *tk)
> +{
> +	unsigned long offset, size, addr;
> +
> +	addr = kallsyms_lookup_name(trace_kprobe_symbol(tk));
> +	addr += trace_kprobe_offset(tk);
> +
> +	if (!kallsyms_lookup_size_offset(addr, &size, &offset))
> +		return true;	/* Out of range. */
> +
> +	return !ftrace_location_range(addr - offset, addr - offset + size);
> +}
> +#else
> +#define within_notrace_func(tk)	(false)
> +#endif
> +
>  /* Internal register function - just handle k*probes and flags */
>  static int __register_trace_kprobe(struct trace_kprobe *tk)
>  {
> @@ -495,6 +512,12 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
>  	if (trace_probe_is_registered(&tk->tp))
>  		return -EINVAL;
>  
> +	if (within_notrace_func(tk)) {
> +		pr_warn("Could not probe notrace function %s\n",
> +			trace_kprobe_symbol(tk));
> +		return -EINVAL;
> +	}
> +
>  	for (i = 0; i < tk->tp.nr_args; i++)
>  		traceprobe_update_arg(&tk->tp.args[i]);
>  
>