From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>,
Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
Song Liu <songliubraving@fb.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
"jani.nikula@linux.intel.com" <jani.nikula@linux.intel.com>,
"joonas.lahtinen@linux.intel.com"
<joonas.lahtinen@linux.intel.com>,
"rodrigo.vivi@intel.com" <rodrigo.vivi@intel.com>,
Alexei Starovoitov <ast@kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
"james.bottomley@hansenpartnership.com"
<james.bottomley@hansenpartnership.com>,
Serge Hallyn <serge@hallyn.com>, James Morris <jmorris@namei.org>,
Will Deacon <will.deacon@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Casey Schaufler <casey@schaufler-ca.com>,
Robert Richter <rric@kernel.org>, Jiri Olsa <jolsa@redhat.com>,
Andi Kleen <ak@linux.intel.com>,
Stephane Eranian <eranian@google.com>,
Igor Lubashev <ilubashe@akamai.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Namhyung Kim <namhyung@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 2/9] perf/core: open access for CAP_SYS_PERFMON privileged process
Date: Mon, 13 Jan 2020 21:17:49 -0800 [thread overview]
Message-ID: <CAADnVQLCtrvvagbbkZG4PyAKb2PWzUouxG3=nxvm8QdpgEWtGQ@mail.gmail.com> (raw)
In-Reply-To: <20200114122506.3cf442dc189a649d4736f86e@kernel.org>
On Mon, Jan 13, 2020 at 7:25 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Sat, 11 Jan 2020 12:57:18 +0300
> Alexey Budankov <alexey.budankov@linux.intel.com> wrote:
>
> >
> > On 11.01.2020 3:35, arnaldo.melo@gmail.com wrote:
>
> > > 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?
> > Could you please also review and comment on patch 5/9 for bpf_trace.c?
>
> As we talked at RFC series of CAP_SYS_TRACING last year, I just expected
> to open it for enabling/disabling kprobes, not for creation.
>
> If we can accept user who has no admin priviledge but the CAP_SYS_PERFMON,
> to shoot their foot by their own risk, I'm OK to allow it. (Even though,
> it should check the max number of probes to be created by something like
> ulimit)
> I think nowadays we have fixed all such kernel crash problems on x86,
> but not sure for other archs, especially on the devices I can not reach.
> I need more help to stabilize it.
I don't see how enable/disable is any safer than creation.
If there are kernel bugs in kprobes the kernel will crash anyway.
I think such partial CAP_SYS_PERFMON would be very confusing to the users.
CAP_* is about delegation of root privileges to non-root.
Delegating some of it is ok, but disallowing creation makes it useless
for bpf tracing, so we would need to add another CAP later.
Hence I suggest to do it right away instead of breaking
sys_perf_even_open() access into two CAPs.
next prev parent reply other threads:[~2020-01-14 5:18 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-18 9:16 [PATCH v4 0/7] Introduce CAP_SYS_PERFMON to secure system performance monitoring and observability Alexey Budankov
2019-12-18 9:24 ` [PATCH v4 1/9] capabilities: introduce CAP_SYS_PERFMON to kernel and user space Alexey Budankov
2019-12-18 19:56 ` Stephen Smalley
2019-12-18 9:25 ` [PATCH v4 2/9] perf/core: open access for CAP_SYS_PERFMON privileged process Alexey Budankov
2020-01-08 16:07 ` Peter Zijlstra
2020-01-09 11:36 ` Alexey Budankov
[not found] ` <20200110140234.GO2844@hirez.programming.kicks-ass.net>
[not found] ` <20200111005213.6dfd98fb36ace098004bde0e@kernel.org>
[not found] ` <20200110164531.GA2598@kernel.org>
[not found] ` <20200111084735.0ff01c758bfbfd0ae2e1f24e@kernel.org>
[not found] ` <2B79131A-3F76-47F5-AAB4-08BCA820473F@fb.com>
[not found] ` <5e191833.1c69fb81.8bc25.a88c@mx.google.com>
2020-01-11 9:57 ` Alexey Budankov
2020-01-13 20:39 ` Song Liu
2020-01-14 3:25 ` Masami Hiramatsu
2020-01-14 5:17 ` Alexei Starovoitov [this message]
2020-01-14 9:47 ` Alexey Budankov
2020-01-14 18:06 ` Alexei Starovoitov
2020-01-14 18:50 ` Alexey Budankov
2020-01-15 1:52 ` Alexei Starovoitov
2020-01-15 5:15 ` Alexey Budankov
2020-04-01 20:50 ` Alexey Budankov
2020-04-03 13:55 ` Alexey Budankov
2020-04-03 13:56 ` Alexey Budankov
2020-01-15 9:45 ` Masami Hiramatsu
2020-01-15 12:11 ` Alexey Budankov
2020-01-14 12:04 ` Masami Hiramatsu
2020-04-01 20:49 ` Alexey Budankov
2020-04-03 14:28 ` Alexey Budankov
2019-12-18 9:26 ` [PATCH v4 3/9] perf tool: extend Perf tool with CAP_SYS_PERFMON capability support Alexey Budankov
2019-12-18 9:27 ` [PATCH v4 4/9] drm/i915/perf: open access for CAP_SYS_PERFMON privileged process Alexey Budankov
2019-12-19 9:10 ` Lionel Landwerlin
2019-12-18 9:28 ` [PATCH v4 5/9] trace/bpf_trace: " Alexey Budankov
2019-12-18 9:28 ` [PATCH v4 6/9] powerpc/perf: " Alexey Budankov
2019-12-18 9:29 ` [PATCH v4 7/9] parisc/perf: " Alexey Budankov
2020-01-27 8:52 ` Helge Deller
2019-12-18 9:30 ` [PATCH v4 8/9] drivers/perf: " Alexey Budankov
[not found] ` <20200117105153.GB6144@willie-the-truck>
2020-01-18 18:48 ` Alexey Budankov
2019-12-18 9:31 ` [PATCH v4 9/9] drivers/oprofile: " Alexey Budankov
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