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

From: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
To: Alexey Budankov <alexey.budankov@linux.intel.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
Subject: Re: [PATCH v8 00/12] Introduce CAP_PERFMON to secure system performance monitoring and observability
Date: Tue, 7 Apr 2020 11:30:14 -0300	[thread overview]
Message-ID: <20200407143014.GD11186@kernel.org> (raw)
In-Reply-To: <f96f8f8a-e65c-3f36-dc85-fc3f5191e8c5@linux.intel.com>

Em Thu, Apr 02, 2020 at 11:42:05AM +0300, Alexey Budankov escreveu:
> This patch set introduces CAP_PERFMON capability designed to secure
> system performance monitoring and observability operations so that
> CAP_PERFMON would assist CAP_SYS_ADMIN capability in its governing role
> for performance monitoring and observability subsystems of the kernel.

So, what am I doing wrong?

[perf@five ~]$ type perf
perf is hashed (/home/perf/bin/perf)
[perf@five ~]$
[perf@five ~]$ ls -lahF /home/perf/bin/perf
-rwxr-x---. 1 root perf_users 24M Apr  7 10:34 /home/perf/bin/perf*
[perf@five ~]$
[perf@five ~]$ getcap /home/perf/bin/perf
[perf@five ~]$ perf top --stdio
Error:
You may not have permission to collect system-wide stats.

Consider tweaking /proc/sys/kernel/perf_event_paranoid,
which controls use of the performance events system by
unprivileged users (without CAP_PERFMON or CAP_SYS_ADMIN).

The current value is 2:

  -1: Allow use of (almost) all events by all users
      Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
>= 0: Disallow ftrace function tracepoint by users without CAP_PERFMON or CAP_SYS_ADMIN
      Disallow raw tracepoint access by users without CAP_SYS_PERFMON or CAP_SYS_ADMIN
>= 1: Disallow CPU event access by users without CAP_PERFMON or CAP_SYS_ADMIN
>= 2: Disallow kernel profiling by users without CAP_PERFMON or CAP_SYS_ADMIN

To make this setting permanent, edit /etc/sysctl.conf too, e.g.:

	kernel.perf_event_paranoid = -1

[perf@five ~]$

Ok, the message says I  need to have CAP_PERFMON, lets do it, using an
unpatched libcap that doesn't know about it but we can use 38,
CAP_PERFMON value instead, and I tested this with a patched libcap as
well, same results:

As root:

[root@five bin]# setcap "38,cap_sys_ptrace,cap_syslog=ep" perf
[root@five bin]#

Back to the 'perf' user in the 'perf_users' group, ok, so now 'perf
record -a' works for system wide sampling of cycles:u, i.e. only
userspace samples, but 'perf top' is failing:

[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 ~]$

- Arnaldo