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Subject: Re: [PATCH v8 00/12] Introduce CAP_PERFMON to secure system
 performance monitoring and observability
To:     Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        James Morris <jmorris@namei.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Serge Hallyn <serge@hallyn.com>, Jiri Olsa <jolsa@redhat.com>,
        Song Liu <songliubraving@fb.com>,
        Andi Kleen <ak@linux.intel.com>,
        Stephane Eranian <eranian@google.com>,
        Igor Lubashev <ilubashe@akamai.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        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>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        linux-man@vger.kernel.org
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 <85da1e42-2cf2-98ca-1e0c-2cf3469b7d30@linux.intel.com>
 <20200407170251.GE12003@kernel.org>
From:   Alexey Budankov <alexey.budankov@linux.intel.com>
Organization: Intel Corp.
Message-ID: <369aaea6-3532-859e-7f1a-4df7806351c5@linux.intel.com>
Date:   Tue, 7 Apr 2020 20:32:00 +0300
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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