linux-kernel - Re: [PATCH v8 00/12] Introduce CAP_PERFMON to secure system performance monitoring and observability

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Date:   Tue, 7 Apr 2020 13:40:50 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        James Morris <jmorris@...ei.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Serge Hallyn <serge@...lyn.com>, Jiri Olsa <jolsa@...hat.com>,
        Song Liu <songliubraving@...com>,
        Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Igor Lubashev <ilubashe@...mai.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        linux-man@...r.kernel.org
Subject: Re: [PATCH v8 00/12] Introduce CAP_PERFMON to secure system
 performance monitoring and observability

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@...e ~]$ type perf
> > >> perf is hashed (/home/perf/bin/perf)
> > >> [perf@...e ~]$ getcap /home/perf/bin/perf
> > >> /home/perf/bin/perf = cap_sys_ptrace,cap_syslog,38+ep
> > >> [perf@...e ~]$ groups
> > >> perf perf_users
> > >> [perf@...e ~]$ 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@...e ~]$ perf top --stdio
> > >> Error:
> > >> Failed to mmap with 1 (Operation not permitted)
> > >> [perf@...e ~]$ 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@...e ~]$ perf evlist
> > >> cycles:u
> > >> [perf@...e ~]$
> > > 
> > > 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@...e ~]$ perf top --stdio -e cycles:u
> > > Error:
> > > Failed to mmap with 1 (Operation not permitted)
> > > [perf@...e ~]$ 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@...e ~]$
> > > 
> > > 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