Re: [PATCH v1 1/3] perf-security: document perf_events/Perf resource control

[Alexey Budankov <alexey.budankov@linux.intel.com>]

On 07.02.2019 2:58, Jonathan Corbet wrote:
> On Fri, 1 Feb 2019 10:29:11 +0300
> Alexey Budankov <alexey.budankov@linux.intel.com> wrote:
> 
>> Extend perf-security.rst file with perf_events/Perf resource control
>> section describing RLIMIT_NOFILE and perf_event_mlock_kb settings for
>> performance monitoring user processes.
>>
>> Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
> 
> Overall these patches seem reasonable, though I have some nits to pick.
> I'm happy to apply them but wouldn't mind an ack from the perf camp.
> 
> Alexey, could you wrap your paragraphs at 72-75 columns?

Sure, let's have it as the forth patch in the series in order not to 
mix the actual content with formatting.

> 
>> ---
>>  Documentation/admin-guide/perf-security.rst | 36 +++++++++++++++++++++
>>  1 file changed, 36 insertions(+)
>>
>> diff --git a/Documentation/admin-guide/perf-security.rst b/Documentation/admin-guide/perf-security.rst
>> index f73ebfe9bfe2..ff6832191577 100644
>> --- a/Documentation/admin-guide/perf-security.rst
>> +++ b/Documentation/admin-guide/perf-security.rst
>> @@ -84,6 +84,40 @@ governed by perf_event_paranoid [2]_ setting:
>>       locking limit is imposed but ignored for unprivileged processes with
>>       CAP_IPC_LOCK capability.
>>  
>> +perf_events/Perf resource control
>> +---------------------------------
>> +
>> +perf_events system call API [2]_ allocates file descriptors for every configured
> 
> *The* perf_events system call API

Accepted.

> 
>> +PMU event. Open file descriptors are a per-process accountable *resource* governed
>> +by RLIMIT_NOFILE [11]_ limit (ulimit -n), which is usually derived from the login
> 
> by *the* RLIMIT_NOFILE

Accepted.

> 
>> +shell process. When configuring Perf collection for a long list of events on a
>> +large server system, this limit can be easily hit preventing required monitoring
>> +configuration. RLIMIT_NOFILE limit can be increased on per-user basis modifying
>> +content of limits.conf file [12]_ on some systems. Ordinary Perf sampling session
> 
> of *the* limits.conf file
> 
> Ordinarily, a Perf

Accepted.

> 
>> +(perf record) requires an amount of open perf_event file descriptors that is not
>> +less than a number of monitored events multiplied by a number of monitored CPUs.
>> +
>> +An amount of memory available to user processes for capturing performance monitoring
>> +data is governed by perf_event_mlock_kb [2]_ setting. This perf_event specific
> 
> by *the* perf_event_mlock_kb

Accepted.

> 
>> +*resource* setting defines overall per-cpu limits of memory allowed for mapping
> 
> Why the *emphasis* here?

Avoided emphasis here and in the other places of this paragraphs.

> 
>> +by the user processes to execute performance monitoring. The setting essentially
>> +extends RLIMIT_MEMLOCK [11]_ limit but only for memory regions mapped specially
> 
> extends *the* RMLIMIT_MEMLOCK limit *,* but only

Accepted.

> 
>> +for capturing monitored performance events and related data.
>> +
>> +For example, if a machine has eight cores and perf_event_mlock_kb limit is set
>> +to 516 KiB then a user process is provided with 516 KiB * 8 = 4128 KiB of memory
> 
> Kib, then

Comma accepted, Kib = 1024 bits and this is not what is meant here - KiB=1024 Bytes.

> 
>> +above RLIMIT_MEMLOCK limit (ulimit -l) for perf_event mmap buffers. In particular
> 
> above *the* RLIMIT_MEMLOCK
> 
> particular,

Accepted.

> 
>> +this means that if the user wants to start two or more performance monitoring
> 
> that, if

Accepted.

> 
>> +processes, it is required to manually distribute available 4128 KiB between the
> 
> s/it is/they are/

Not sure what you mean here. I want to say that the users is required to distribute 
memory among the processes using --mmap-pages. Replaced 'it' with 'the user'.

> 
>> +monitoring processes, for example, using --mmap-pages Perf record mode option.
> 
> using *the* --mmap-pages option

Accepted.

> 
>> +Otherwise, the first started performance monitoring process allocates all available
>> +4128 KiB and the other processes will fail to proceed due to the lack of memory.
>> +
>> +RLIMIT_MEMLOCK and perf_event_mlock_kb *resource* constraints are ignored for
>> +processes with CAP_IPC_LOCK capability. Thus, perf_events/Perf privileged users
> 
> with *the* CAP_IPC_LOCK

Accepted.

> 
>> +can be provided with memory above the constraints for perf_events/Perf performance
>> +monitoring purpose by providing the Perf executable with CAP_IPC_LOCK capability.
>> +
>>  Bibliography
>>  ------------
>>  
>> @@ -94,4 +128,6 @@ Bibliography
>>  .. [5] `<https://www.kernel.org/doc/html/latest/security/credentials.html>`_
>>  .. [6] `<http://man7.org/linux/man-pages/man7/capabilities.7.html>`_
>>  .. [7] `<http://man7.org/linux/man-pages/man2/ptrace.2.html>`_
>> +.. [11] `<http://man7.org/linux/man-pages/man2/getrlimit.2.html>`_
>> +.. [12] `<http://man7.org/linux/man-pages/man5/limits.conf.5.html>`_
> 
> Thanks,
> 
> jon
> 

Thanks,
Alexey