Re: [PATCH v4 2/9] perf/core: open access for CAP_SYS_PERFMON privileged process

[Alexey Budankov]

On 11.01.2020 3:35, arnaldo.melo@xxxxxxxxx wrote:
> <keescook@xxxxxxxxxxxx>,Jann Horn <jannh@xxxxxxxxxx>,Thomas Gleixner <tglx@xxxxxxxxxxxxx>,Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>,Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>,linux-kernel <linux-kernel@xxxxxxxxxxxxxxx>,"linux-security-module@xxxxxxxxxxxxxxx" <linux-security-module@xxxxxxxxxxxxxxx>,"selinux@xxxxxxxxxxxxxxx" <selinux@xxxxxxxxxxxxxxx>,"intel-gfx@xxxxxxxxxxxxxxxxxxxxx" <intel-gfx@xxxxxxxxxxxxxxxxxxxxx>,"bpf@xxxxxxxxxxxxxxx" <bpf@xxxxxxxxxxxxxxx>,"linux-parisc@xxxxxxxxxxxxxxx" <linux-parisc@xxxxxxxxxxxxxxx>,"linuxppc-dev@xxxxxxxxxxxxxxxx" <linuxppc-dev@xxxxxxxxxxxxxxxx>,"linux-perf-users@xxxxxxxxxxxxxxx" <linux-perf-users@xxxxxxxxxxxxxxx>,"linux-arm-kernel@xxxxxxxxxxxxxxxxxxx" <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>,"oprofile-list@xxxxxxxxxxxx" <oprofile-list@xxxxxxxxxxxx>
> From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Message-ID: <A7F0BF73-9189-44BA-9264-C88F2F51CBF3@xxxxxxxxxx>
> 
> On January 10, 2020 9:23:27 PM GMT-03:00, Song Liu <songliubraving@xxxxxx> wrote:
>>
>>
>>> On Jan 10, 2020, at 3:47 PM, Masami Hiramatsu <mhiramat@xxxxxxxxxx>
>> wrote:
>>>
>>> On Fri, 10 Jan 2020 13:45:31 -0300
>>> Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
>>>
>>>> Em Sat, Jan 11, 2020 at 12:52:13AM +0900, Masami Hiramatsu escreveu:
>>>>> On Fri, 10 Jan 2020 15:02:34 +0100 Peter Zijlstra
>> <peterz@xxxxxxxxxxxxx> wrote:
>>>>>> Again, this only allows attaching to previously created kprobes,
>> it does
>>>>>> not allow creating kprobes, right?
>>>>
>>>>>> That is; I don't think CAP_SYS_PERFMON should be allowed to create
>>>>>> kprobes.
>>>>
>>>>>> As might be clear; I don't actually know what the user-ABI is for
>>>>>> creating kprobes.
>>>>
>>>>> There are 2 ABIs nowadays, ftrace and ebpf. perf-probe uses ftrace
>> interface to
>>>>> define new kprobe events, and those events are treated as
>> completely same as
>>>>> tracepoint events. On the other hand, ebpf tries to define new
>> probe event
>>>>> via perf_event interface. Above one is that interface. IOW, it
>> creates new kprobe.
>>>>
>>>> Masami, any plans to make 'perf probe' use the perf_event_open()
>>>> interface for creating kprobes/uprobes?
>>>
>>> Would you mean perf probe to switch to perf_event_open()?
>>> No, perf probe is for setting up the ftrace probe events. I think we
>> can add an
>>> option to use perf_event_open(). But current kprobe creation from
>> perf_event_open()
>>> is separated from ftrace by design.
>>
>> I guess we can extend event parser to understand kprobe directly.
>> Instead of
>>
>> 	perf probe kernel_func
>> 	perf stat/record -e probe:kernel_func ...
>>
>> We can just do 
>>
>> 	perf stat/record -e kprobe:kernel_func ...
> 
> 
> You took the words from my mouth, exactly, that is a perfect use case, an alternative to the 'perf probe' one of making a disabled event that then gets activated via record/stat/trace, in many cases it's better, removes the explicit probe setup case.

Arnaldo, Masami, Song,

What do you think about making this also open to CAP_SYS_PERFMON privileged processes?
Could you please also review and comment on patch 5/9 for bpf_trace.c?

Thanks,
Alexey

> 
> Regards, 
> 
> - Arnaldo
> 
>>
>> Thanks,
>> Song
>