linux-kernel - RE: [PATCH v2] tracing: precise log info for kretprobe addr err

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Message-ID: <AM6PR08MB3589CB4AB4EC3ADBBB45144C98BF0@AM6PR08MB3589.eurprd08.prod.outlook.com>
Date:   Sat, 23 Jan 2021 14:21:48 +0000
From:   Jianlin Lv <Jianlin.Lv@....com>
To:     Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
CC:     "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "oleg@...hat.com" <oleg@...hat.com>
Subject: RE: [PATCH v2] tracing: precise log info for kretprobe addr err



> -----Original Message-----
> From: Masami Hiramatsu <mhiramat@...nel.org>
> Sent: Thursday, January 21, 2021 10:29 AM
> To: Steven Rostedt <rostedt@...dmis.org>
> Cc: Jianlin Lv <Jianlin.Lv@....com>; mingo@...hat.com; linux-
> kernel@...r.kernel.org; Masami Hiramatsu <mhiramat@...nel.org>;
> oleg@...hat.com
> Subject: Re: [PATCH v2] tracing: precise log info for kretprobe addr err
>
> On Wed, 20 Jan 2021 11:20:04 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
>
> >
> > You forgot to include Masami on Cc again. Masami maintains kprobes.
> > Please include him on any updates, as he needs to review them, and
> > give his acknowledgment before acceptance.
> >
> > I need to update MAINTAINERS files to include trace_kprobe under
> KPROBES.
> > And I also don't see any UPROBES section there. That needs to be done
> > as well.

Regarding the UPROBES, I read the code of trace_uprobe_create() and  found a place for improvement.

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 3cf7128e1ad3..8c81f04d7755 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -567,16 +567,18 @@ static int trace_uprobe_create(int argc, const char **argv)
        if (!filename)
                return -ENOMEM;

+       trace_probe_log_init("trace_uprobe", argc, argv);
+       trace_probe_log_set_index(1);   /* filename is the 2nd argument */
+
        /* Find the last occurrence, in case the path contains ':' too. */
        arg = strrchr(filename, ':');
        if (!arg || !isdigit(arg[1])) {
+               trace_probe_log_err(arg + 1 - filename, BAD_UPROBE_OFFS);
                kfree(filename);
-               return -ECANCELED;
+               ret = -EINVAL;
+               goto out;
        }

-       trace_probe_log_init("trace_uprobe", argc, argv);
-       trace_probe_log_set_index(1);   /* filename is the 2nd argument */
-

Is there anything else that is missing?
Could you provide more detailed guidance?


>
> Uprobes is under kernel/events/, which seems to be handled by
> performance event subsystem. Maybe we should ask them too.
> Or, can I be a reviewer (R:) for tracing subsystem?
>
> >
> > On Wed, 20 Jan 2021 23:56:44 +0800
> > Jianlin Lv <Jianlin.Lv@....com> 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
> > >                        ^
> > >
> > > Signed-off-by: Jianlin Lv <Jianlin.Lv@....com>
> > >
> > > v2:add !strchr(symbol, ':') to check really bad symbol or not.
> >
> > Also, the "changes since" section should be below the "---" so that
> > they don't get pulled into the commit.
>
> Except that, this looks good to me.
>
> Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
>
> Thank you,
>
> >
> > Thanks!
> >
> > -- Steve
> >
> >
> > > ---
> > >  kernel/trace/trace_kprobe.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/kernel/trace/trace_kprobe.c
> > > b/kernel/trace/trace_kprobe.c index e6fba1798771..bce63d5ecaec
> > > 100644
> > > --- 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)) {
> > >  trace_probe_log_err(0, BAD_RETPROBE);
> > >  goto parse_error;
> > >  }
> >
>
>
> --
> Masami Hiramatsu <mhiramat@...nel.org>
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