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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 20:02, Arnaldo Carvalho de Melo wrote:
> Em Tue, Apr 07, 2020 at 07:52:56PM +0300, Alexey Budankov escreveu:
>>
>> On 07.04.2020 19:36, Arnaldo Carvalho de Melo wrote:
>>> Em Tue, Apr 07, 2020 at 05:54:27PM +0300, Alexey Budankov escreveu:
>>>> 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:
>
>> Looks like top mode somehow reaches perf mmap limit described here [1].
>> Using -m option solves the issue avoiding cap_ipc_lock on my 8 cores machine:
>> perf top -e cycles -m 1
>
> So this would read better?
>
> diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst
> index ed33682e26b0..d44dd24b0244 100644
> --- a/Documentation/admin-guide/perf-security.rst
> +++ b/Documentation/admin-guide/perf-security.rst
> @@ -127,8 +127,8 @@ taken to create such groups of privileged Perf users.
>
> ::
>
> - # 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
> + # setcap "cap_perfmon,cap_sys_ptrace,cap_syslog=ep" perf
> + # setcap -v "cap_perfmon,cap_sys_ptrace,cap_syslog=ep" perf
> perf: OK
> # getcap perf
> perf = cap_sys_ptrace,cap_syslog,cap_perfmon+ep
> @@ -140,6 +140,10 @@ i.e.:
>
> # setcap "38,cap_ipc_lock,cap_sys_ptrace,cap_syslog=ep" perf
>
> +Note that you may need to have 'cap_ipc_lock' in the mix for tools such as
> +'perf top', alternatively use 'perf top -m N', to reduce the memory that
> +it uses for the perf ring buffer, see the memory allocation section below.
> +

Let's stay with the first variant of you addition to this patch and also
extend the paragraph below as suggested in other mail in the thread.

> 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
>

Thanks,
Alexey

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