On Mon, 25 Jan 2021 13:38:40 -0500
Steven Rostedt <rost...@goodmis.org> wrote:
> On Mon, 25 Jan 2021 19:19:27 +0100
> Oleg Nesterov <o...@redhat.com> wrote:
>
> > On 01/26, Jianlin Lv wrote:
> > >
> > > When trying to create kretprobe with the wrong function symbol in tracefs;
> > > The error is triggered in the register_trace_kprobe() and recorded as
> > > FAIL_REG_PROBE issue,
> > >
> > > Example:
> > > $ cd /sys/kernel/debug/tracing
> > > $ echo 'r:myprobe ERROR_SYMBOL_XXX ret=%x0' >> kprobe_events
> > > bash: echo: write error: Invalid argument
> > > $ cat error_log
> > > [142797.347877] trace_kprobe: error: Failed to register probe event
> > > Command: r:myprobe ERROR_SYMBOL_XXX ret=%x0
> > > ^
> > >
> > > This error can be detected in the parameter parsing stage, the effect of
> > > applying this patch is as follows:
> > >
> > > $ echo 'r:myprobe ERROR_SYMBOL_XXX ret=%x0' >> kprobe_events
> > > bash: echo: write error: Invalid argument
> > > $ cat error_log
> > > [415.89]trace_kprobe: error: Retprobe address must be an function
> > > entry
> > > Command: r:myprobe ERROR_SYMBOL_XXX ret=%x0
> >
> > IOW, the "offset != 0" check removed by this patch is obviously wrong,
> > right?
> >
No, not wrong. Even offset != 0, if the symbol exists in the kernel,
kprobe_on_func_entry() will check it.
> > Agreed, but...
> >
> > > --- a/kernel/trace/trace_kprobe.c
> > > +++ b/kernel/trace/trace_kprobe.c
> > > @@ -830,7 +830,7 @@ static int trace_kprobe_create(int argc, const char
> > > *argv[])
> > > flags |= TPARG_FL_RETURN;
> > > if (kprobe_on_func_entry(NULL, symbol, offset))
> > > flags |= TPARG_FL_FENTRY;
> > > - if (offset && is_return && !(flags & TPARG_FL_FENTRY)) {
> > > + if (!strchr(symbol, ':') && is_return && !(flags &
> > > TPARG_FL_FENTRY)) {
> >
> > but why did you add the strchr(':') check instead?
> >
> > I was really puzzled until I found the this email from Masami:
> > https://lore.kernel.org/lkml/20210120131406.5a992c1e434681750a0cd...@kernel.org/
> >
> > So I leave this to you and Masami, but perhaps you can document this check
> > at
> > least in the changelog?
> >
>
> No, you are correct. That needs to be documented in the code.
Agreed. There should be commented that is defered until the module is loaded.
>
> I was about to comment that the check requires a comment ;-)
>
> Jianlin,
>
> Care to send a v4 of the patch with a comment to why we are checking the
> symbol for ':'.
Thank you!
>
> Thanks!
>
> -- Steve
>
--
Masami Hiramatsu <mhira...@kernel.org>
