Re: [PATCH v1 3/3] perf-security: document perf_events/Perf resource control
From: Alexey Budankov
Date: Thu Feb 07 2019 - 08:14:25 EST
On 07.02.2019 3:01, Jonathan Corbet wrote:
> On Fri, 1 Feb 2019 10:30:58 +0300
> Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx> wrote:
>> Elaborate on possible perf_event/Perf privileged users groups
>> and document steps about creating such groups.
>> Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
>> 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
>> + 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.