From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey Budankov Subject: Re: [PATCH v1 3/3] perf-security: document perf_events/Perf resource control References: <9cfbf7a1-72dd-f9d0-8137-0f120fa74d21@linux.intel.com> <5ac4b7aa-b640-d8a4-1926-cf612fada974@linux.intel.com> <20190206170151.00c92333@lwn.net> Message-ID: Date: Thu, 7 Feb 2019 16:14:16 +0300 MIME-Version: 1.0 In-Reply-To: <20190206170151.00c92333@lwn.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit To: Jonathan Corbet Cc: Kees Cook , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Jann Horn , Arnaldo Carvalho de Melo , Jiri Olsa , Namhyung Kim , Alexander Shishkin , Mark Rutland , Andi Kleen , Tvrtko Ursulin , "kernel-hardening@lists.openwall.com" , "linux-doc@vger.kernel.org" , linux-kernel List-ID: On 07.02.2019 3:01, Jonathan Corbet wrote: > On Fri, 1 Feb 2019 10:30:58 +0300 > Alexey Budankov wrote: > >> Elaborate on possible perf_event/Perf privileged users groups >> and document steps about creating such groups. >> >> Signed-off-by: Alexey Budankov >> --- >> Documentation/admin-guide/perf-security.rst | 43 +++++++++++++++++++++ >> 1 file changed, 43 insertions(+) >> >> diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst >> index 7da7fa459718..fe90f8952be9 100644 >> --- a/Documentation/admin-guide/perf-security.rst >> +++ b/Documentation/admin-guide/perf-security.rst >> @@ -73,6 +73,48 @@ enable capturing of additional data required for later performance analysis of >> monitored processes or a system. For example, CAP_SYSLOG capability permits >> reading kernel space memory addresses from /proc/kallsyms file. >> >> +perf_events/Perf privileged users >> +--------------------------------- >> + >> +Mechanisms of capabilities, privileged capability-dumb files [6]_ and file system >> +ACLs [10]_ can be used to create a dedicated group of perf_events/Perf privileged >> +users who are permitted to execute performance monitoring without *scope* limits. >> +The following steps can be taken to create such a group of privileged Perf user >> + >> +1. Create perf_users group of privileged Perf users, assign perf_users group to >> + Perf tool executable and limit *access* to the executable for other users in >> + the system: >> + >> +:: >> + >> + # groupadd perf_users >> + # ls -alhF >> + -rwxr-xr-x 2 root root 11M Oct 19 15:12 perf >> + # chgrp perf_users perf >> + # ls -alhF >> + -rwxr-xr-x 2 root perf_users 11M Oct 19 15:12 perf >> + # chmod o-rwx perf >> + # ls -alhF >> + -rwxr-x--- 2 root perf_users 11M Oct 19 15:12 perf > > Since we're giving basic sysadmin info here, we should probably say > explicitly that this will block access to the perf binary to anybody who > is not in the perf_users group. We already say that above: "limit *access* to the executable for other users in the system". Let's have it this way then: "limit access to the executable for other users in the system who are not in the perf_users group". > >> +2. Assign required capabilities to the Perf tool executable file and enable > > Assign *the* required Accepted. > >> + members of perf_users group with performance monitoring privileges [6]_ : >> + >> +:: >> + >> + # setcap "cap_sys_admin,cap_sys_ptrace,cap_syslog=ep" perf >> + # setcap -v "cap_sys_admin,cap_sys_ptrace,cap_syslog=ep" perf >> + perf: OK >> + # getcap perf >> + perf = cap_sys_ptrace,cap_sys_admin,cap_syslog+ep >> + >> +As a result, members of perf_users group are capable of conducting performance >> +monitoring by using functionality of the configured Perf tool executable that, >> +when executes, passes perf_events subsystem *scope* checks. >> + >> +This specific *access* control management is only available to superuser or root > > Why the *emphasis* here? We prefer to minimize this kind of markup > whenever possible. Avoided emphasis here and in the other places of this paragraph. > > Thanks, > > jon > Thanks, Alexey