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

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Date:   Mon, 13 Jan 2020 20:39:10 +0000
From:   Song Liu <songliubraving@...com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
CC:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        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 Jan 11, 2020, at 1:57 AM, Alexey Budankov <alexey.budankov@...ux.intel.com> wrote:
> 
> 
> 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?

I think we should at least allow CAP_SYS_PERFMON to create some kprobes. Maybe we can 
limited that to per-task kprobes, and the task should be owned by the user?

Thanks,
Song