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SubjectRe: [PATCH v8 00/12] Introduce CAP_PERFMON to secure system performance monitoring and observability
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On 07.04.2020 19:40, Arnaldo Carvalho de Melo wrote:
> Em Tue, Apr 07, 2020 at 01:36:54PM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Tue, Apr 07, 2020 at 05:54:27PM +0300, Alexey Budankov escreveu:
>>> On 07.04.2020 17:35, Arnaldo Carvalho de Melo wrote:
>>>> Em Tue, Apr 07, 2020 at 11:30:14AM -0300, Arnaldo Carvalho de Melo escreveu:
>>>>> [perf@five ~]$ type perf
>>>>> perf is hashed (/home/perf/bin/perf)
>>>>> [perf@five ~]$ getcap /home/perf/bin/perf
>>>>> /home/perf/bin/perf = cap_sys_ptrace,cap_syslog,38+ep
>>>>> [perf@five ~]$ groups
>>>>> perf perf_users
>>>>> [perf@five ~]$ id
>>>>> uid=1002(perf) gid=1002(perf) groups=1002(perf),1003(perf_users) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
>>>>> [perf@five ~]$ perf top --stdio
>>>>> Error:
>>>>> Failed to mmap with 1 (Operation not permitted)
>>>>> [perf@five ~]$ perf record -a
>>>>> ^C[ perf record: Woken up 1 times to write data ]
>>>>> [ perf record: Captured and wrote 1.177 MB perf.data (1552 samples) ]
>>>>>
>>>>> [perf@five ~]$ perf evlist
>>>>> cycles:u
>>>>> [perf@five ~]$
>>>>
>>>> Humm, perf record falls back to cycles:u after initially trying cycles
>>>> (i.e. kernel and userspace), lemme see trying 'perf top -e cycles:u',
>>>> lemme test, humm not really:
>>>>
>>>> [perf@five ~]$ perf top --stdio -e cycles:u
>>>> Error:
>>>> Failed to mmap with 1 (Operation not permitted)
>>>> [perf@five ~]$ perf record -e cycles:u -a sleep 1
>>>> [ perf record: Woken up 1 times to write data ]
>>>> [ perf record: Captured and wrote 1.123 MB perf.data (132 samples) ]
>>>> [perf@five ~]$
>>>>
>>>> Back to debugging this.
>>>
>>> Could makes sense adding cap_ipc_lock to the binary to isolate from this:
>>>
>>> kernel/events/core.c: 6101
>>> if ((locked > lock_limit) && perf_is_paranoid() &&
>>> !capable(CAP_IPC_LOCK)) {
>>> ret = -EPERM;
>>> goto unlock;
>>> }
>>
>>
>> That did the trick, I'll update the documentation and include in my
>> "Committer testing" section:
>
> I ammended this to that patch, please check the wording:
>
> - Arnaldo
>
> diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst
> index c0ca0c1a6804..ed33682e26b0 100644
> --- a/Documentation/admin-guide/perf-security.rst
> +++ b/Documentation/admin-guide/perf-security.rst
> @@ -127,12 +127,19 @@ taken to create such groups of privileged Perf users.
>
> ::
>
> - # setcap "cap_perfmon,cap_sys_ptrace,cap_syslog=ep" perf
> - # setcap -v "cap_perfmon,cap_sys_ptrace,cap_syslog=ep" perf
> + # setcap "cap_perfmon,cap_ipc_lock,cap_sys_ptrace,cap_syslog=ep" perf
> + # setcap -v "cap_perfmon,cap_ipc_lock,cap_sys_ptrace,cap_syslog=ep" perf
> perf: OK
> # getcap perf
> perf = cap_sys_ptrace,cap_syslog,cap_perfmon+ep
>
> +If the libcap installed doesn't yet support "cap_perfmon", use "38" instead,
> +i.e.:
> +
> +::
> +
> + # setcap "38,cap_ipc_lock,cap_sys_ptrace,cap_syslog=ep" perf
> +
> As a result, members of perf_users group are capable of conducting
> performance monitoring and observability by using functionality of the
> configured Perf tool executable that, when executes, passes perf_events
>

Looks good to me. The paragraph just above should then also be extended to
mention that perf_events subsystem memory limit is ignored due to usage of
CAP_IPC_LOCK:

"As a result, members of perf_users group are capable of conducting
performance monitoring and observability by using functionality of the
configured Perf tool executable that, when executes, passes perf_events
subsystem scope and perf_event_mlock_kb locking limit checks."

~Alexey

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