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

[Song Liu <songliubraving@fb.com>]

> On Jan 11, 2020, at 1:57 AM, Alexey Budankov <alexey.budankov@linux.intel.com> wrote:
> 
> 
> On 11.01.2020 3:35, arnaldo.melo@gmail.com wrote:
>> <keescook@chromium.org>,Jann Horn <jannh@google.com>,Thomas Gleixner <tglx@linutronix.de>,Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,Lionel Landwerlin <lionel.g.landwerlin@intel.com>,linux-kernel <linux-kernel@vger.kernel.org>,"linux-security-module@vger.kernel.org" <linux-security-module@vger.kernel.org>,"selinux@vger.kernel.org" <selinux@vger.kernel.org>,"intel-gfx@lists.freedesktop.org" <intel-gfx@lists.freedesktop.org>,"bpf@vger.kernel.org" <bpf@vger.kernel.org>,"linux-parisc@vger.kernel.org" <linux-parisc@vger.kernel.org>,"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,"linux-perf-users@vger.kernel.org" <linux-perf-users@vger.kernel.org>,"linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>,"oprofile-list@lists.sf.net" <oprofile-list@lists.sf.net>
>> From: Arnaldo Carvalho de Melo <acme@kernel.org>
>> Message-ID: <A7F0BF73-9189-44BA-9264-C88F2F51CBF3@kernel.org>
>> 
>> On January 10, 2020 9:23:27 PM GMT-03:00, Song Liu <songliubraving@fb.com> wrote:
>>> 
>>> 
>>>> On Jan 10, 2020, at 3:47 PM, Masami Hiramatsu <mhiramat@kernel.org>
>>> wrote:
>>>> 
>>>> On Fri, 10 Jan 2020 13:45:31 -0300
>>>> Arnaldo Carvalho de Melo <acme@kernel.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@infradead.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