Date: Thu, 7 Feb 2019 16:14:16 +0300 From: Alexey Budankov <alexey.budankov@...ux.intel.com> To: Jonathan Corbet <corbet@....net> Cc: Kees Cook <keescook@...omium.org>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, Jann Horn <jannh@...gle.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Mark Rutland <mark.rutland@....com>, Andi Kleen <ak@...ux.intel.com>, Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v1 3/3] perf-security: document perf_events/Perf resource control On 07.02.2019 3:01, Jonathan Corbet wrote: > On Fri, 1 Feb 2019 10:30:58 +0300 > Alexey Budankov <alexey.budankov@...ux.intel.com> wrote: > >> Elaborate on possible perf_event/Perf privileged users groups >> and document steps about creating such groups. >> >> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com> >> --- >> 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 _ and file system >> +ACLs _ 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 _ : >> + >> +:: >> + >> + # 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
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