linux-kernel - Re: [PATCH v4 2/9] perf/core: open access for CAP_SYS

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Date:   Sat, 11 Jan 2020 12:57:18 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     arnaldo.melo@...il.com, Song Liu <songliubraving@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        "jani.nikula@...ux.intel.com" <jani.nikula@...ux.intel.com>,
        "joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
        "rodrigo.vivi@...el.com" <rodrigo.vivi@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "james.bottomley@...senpartnership.com" 
        <james.bottomley@...senpartnership.com>,
        Serge Hallyn <serge@...lyn.com>,
        James Morris <jmorris@...ei.org>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Robert Richter <rric@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Igor Lubashev <ilubashe@...mai.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/9] perf/core: open access for CAP_SYS_PERFMON
 privileged process


On 11.01.2020 3:35, arnaldo.melo@...il.com wrote:
> <keescook@...omium.org>,Jann Horn <jannh@...gle.com>,Thomas Gleixner <tglx@...utronix.de>,Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,Lionel Landwerlin <lionel.g.landwerlin@...el.com>,linux-kernel <linux-kernel@...r.kernel.org>,"linux-security-module@...r.kernel.org" <linux-security-module@...r.kernel.org>,"selinux@...r.kernel.org" <selinux@...r.kernel.org>,"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,"bpf@...r.kernel.org" <bpf@...r.kernel.org>,"linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,"linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,"oprofile-list@...ts.sf.net" <oprofile-list@...ts.sf.net>
> From: Arnaldo Carvalho de Melo <acme@...nel.org>
> Message-ID: <A7F0BF73-9189-44BA-9264-C88F2F51CBF3@...nel.org>
> 
> On January 10, 2020 9:23:27 PM GMT-03:00, Song Liu <songliubraving@...com> wrote:
>>
>>
>>> On Jan 10, 2020, at 3:47 PM, Masami Hiramatsu <mhiramat@...nel.org>
>> wrote:
>>>
>>> On Fri, 10 Jan 2020 13:45:31 -0300
>>> Arnaldo Carvalho de Melo <acme@...nel.org> 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@...radead.org> 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
>