From: Alexey Budankov <alexey.budankov@linux.intel.com>
To: Masami Hiramatsu <mhiramat@kernel.org>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
Song Liu <songliubraving@fb.com>, 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: Wed, 15 Jan 2020 15:11:06 +0300 [thread overview]
Message-ID: <2610ef96-40c4-5ff1-f972-104d418a3ac8@linux.intel.com> (raw)
In-Reply-To: <20200115184538.bb8604e914dcc0eaeaf357fd@kernel.org>
On 15.01.2020 12:45, Masami Hiramatsu wrote:
> On Tue, 14 Jan 2020 21:50:33 +0300
> Alexey Budankov <alexey.budankov@linux.intel.com> wrote:
>
>>
>> On 14.01.2020 21:06, Alexei Starovoitov wrote:
>>> On Tue, Jan 14, 2020 at 1:47 AM Alexey Budankov
>>> <alexey.budankov@linux.intel.com> wrote:
>>>>>>
>>>>>> 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.
>>>>>
>>>>
>>>> Alexei, Masami,
>>>>
>>>> Thanks for your meaningful input.
>>>> If we know in advance that it still can crash the system in some cases and on
>>>> some archs, even though root fully controls delegation thru CAP_SYS_PERFMON,
>>>> such delegation looks premature until the crashes are avoided. So it looks like
>>>> access to eBPF for CAP_SYS_PERFMON privileged processes is the subject for
>>>> a separate patch set.
>>>
>>> perf_event_open is always dangerous. sw cannot guarantee non-bugginess of hw.
>>
>
> OK, anyway, for higher security, admin may not give CAP_SYS_PERFMON to
> unpriviledged users, since it might allows users to analyze kernel, which
> can lead security concerns.
FWIW,
Discovered security related hardware issues could be mitigated in software and
here [1] is the official procedure documented on how to follow up, so this could
be a draft plan to approach eBPF perf_events related hardware issues, if required.
[1] https://www.kernel.org/doc/html/latest/process/embargoed-hardware-issues.html
>
>> Sure, software cannot guarantee, but known software bugs could still be fixed,
>> that's what I meant.
>
> Agreed, bugs must be fixed anyway.
>
> Thank you,
>
>>> imo adding a cap just for pmc is pointless.
>>> if you add a new cap it should cover all of sys_perf_event_open syscall.
>>> subdividing it into sw vs hw counters, kprobe create vs enable, etc will
>>> be the source of ongoing confusion. nack to such cap.
>>>
>>
>> Well, as this patch set already covers complete perf_event_open functionality,
>> and also eBPF related parts too, could you please review and comment on it?
>> Does the patches 2/9 and 5/9 already bring all required extentions?
>>
>> Thanks,
>> Alexey
>
>
next prev parent reply other threads:[~2020-01-15 12:11 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
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 [this message]
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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