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Message-ID: <20190206170151.00c92333@lwn.net>
Date: Wed, 6 Feb 2019 17:01:51 -0700
From: Jonathan Corbet <corbet@....net>
To: Alexey Budankov <alexey.budankov@...ux.intel.com>
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 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 [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 users.
> +
> +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.
> +2. Assign required capabilities to the Perf tool executable file and enable
Assign *the* required
> + 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.
Thanks,
jon
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