lkml.org 
[lkml]   [2018]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/2] kprobe: fix: Add ftrace_ops_assist_func to kprobe blacklist
On Fri, 16 Mar 2018 23:01:54 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Sat, 17 Mar 2018 10:22:11 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> > Or, we can check it by ftrace_location_range() as below patch.
>
> Cute ;-)
>
> >
> > 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@kernel.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@kernel.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;
> > + }
>
> This will prevent probing assembly code. Do we want to do that? Or is
> kprobes already prohibited from doing so?

No, kprobes itself can probe any assembly code except for the area where
can cause recursive hit as I explained. So anyway we still need to
mark those functions NOKPROBE_SYMBOL.

And note that this just prevent to probe those notrace code *via kprobe_events*
interface. So pure kprobe user (like systemtap) is not effected by this change.

So, maybe we would better to provide another debug knob which skips above check.
This is only for non-experienced admins :)

Thanks,

>
> -- Steve
>
>
> > +
> > for (i = 0; i < tk->tp.nr_args; i++)
> > traceprobe_update_arg(&tk->tp.args[i]);
> >
> >
>


--
Masami Hiramatsu <mhiramat@kernel.org>

\
 
 \ /
  Last update: 2018-03-17 08:58    [W:0.154 / U:3.956 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site