linux-kernel - Re: [PATCH 2/2] trace_uprobe: Simplify probes_seq

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Date:   Tue, 6 Mar 2018 14:04:20 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Cc:     wangnan0 <wangnan0@...wei.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
        Namhyung Kim <namhyung@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] trace_uprobe: Simplify probes_seq_show()

On Tue, Mar 6, 2018 at 12:12 AM, Ravi Bangoria
<ravi.bangoria@...ux.vnet.ibm.com> wrote:
>
>
> On 02/08/2018 09:13 AM, Ravi Bangoria wrote:
>>
>> On 02/08/2018 08:59 AM, Kees Cook wrote:
>>> On Tue, Feb 6, 2018 at 8:34 PM, Ravi Bangoria
>>> <ravi.bangoria@...ux.vnet.ibm.com> wrote:
>>>> Simplify probes_seq_show() function. We are using %lx to display
>>>> the offset and we don't prepend unnecessary 0s in the offset.
>>>>
>>>> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
>>>> ---
>>>>  kernel/trace/trace_uprobe.c | 21 +++------------------
>>>>  1 file changed, 3 insertions(+), 18 deletions(-)
>>>>
>>>> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
>>>> index c2c965398893..c12a3957e1ee 100644
>>>> --- a/kernel/trace/trace_uprobe.c
>>>> +++ b/kernel/trace/trace_uprobe.c
>>>> @@ -602,24 +602,9 @@ static int probes_seq_show(struct seq_file *m, void *v)
>>>>         char c = is_ret_probe(tu) ? 'r' : 'p';
>>>>         int i;
>>>>
>>>> -       seq_printf(m, "%c:%s/%s", c, tu->tp.call.class->system,
>>>> -                       trace_event_name(&tu->tp.call));
>>>> -       seq_printf(m, " %s:", tu->filename);
>>>> -
>>>> -       /* Don't print "0x  (null)" when offset is 0 */
>>>> -       if (tu->offset) {
>>>> -               seq_printf(m, "0x%lx", tu->offset);
>>>> -       } else {
>>>> -               switch (sizeof(void *)) {
>>>> -               case 4:
>>>> -                       seq_printf(m, "0x00000000");
>>>> -                       break;
>>>> -               case 8:
>>>> -               default:
>>>> -                       seq_printf(m, "0x0000000000000000");
>>>> -                       break;
>>>> -               }
>>>> -       }
>>>> +       seq_printf(m, "%c:%s/%s %s:0x%lx", c, tu->tp.call.class->system,
>>>> +                       trace_event_name(&tu->tp.call), tu->filename,
>>>> +                       tu->offset);
>>> To keep the prepended zeros (and avoid the redundant 0x prefix):
>>>
>>> "...%#0*lx...", ... sizeof(void *) * 2, tu->offset);
>>>
>>> As in:
>>>
>>> +       seq_printf(m, "%c:%s/%s %s:%#0*lx", c, tu->tp.call.class->system,
>>> +                       trace_event_name(&tu->tp.call), tu->filename,
>>> +                       sizeof(void *) * 2, tu->offset);
>> This is useful, thanks Kees.
>>
>> @Wang, Do we really need those 0s? Won't just 0x0 should
>> suffice? Here is the sample output...
>>
>>   # echo "p:probe_a/main /tmp/a.out:0x0" > uprobe_events
>>
>> Before patch:
>>   # cat uprobe_events
>>     p:probe_a/main /tmp/a.out:0x0000000000000000
>>
>> After patch:
>>   # cat uprobe_events
>>     p:probe_a/main /tmp/a.out:0x0
>
> Wang, ping :)
>
> Kees, I don't hear back from Wang and no one has reported any issues with
> the patches yet. Can I have your Acked-by?

I didn't see a v2 of these patches with the output fixed?

-Kees

-- 
Kees Cook
Pixel Security