linux-kernel - Re: [PATCH v1 2/2]: Documentation/admin-guide: introduce perf-security.rst file

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Date:   Mon, 19 Nov 2018 18:13:16 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Jonatan Corbet <corbet@....net>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Tvrtko Ursulin <tursulin@...ulin.net>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com, linux-doc@...r.kernel.org
Subject: Re: [PATCH v1 2/2]: Documentation/admin-guide: introduce
 perf-security.rst file

Hi,
On 19.11.2018 13:33, Peter Zijlstra wrote:
> On Mon, Nov 19, 2018 at 08:42:52AM +0300, Alexey Budankov wrote:
>>
>> Implement initial version of perf-security.rst documentation file 
>> initially covering security concerns related to PCL/Perf performance 
>> monitoring in multiuser environments.
> 
> Ditch the PCL thing. That's not a term used anywhere in the kernel.

Ok. Which is the proper wording to reference to Perf kernel subsystem?

> 
> Also:
> 
>> +PCL/Perf unprivileged users
>> +---------------------------
>> +
>> +PCL/Perf *scope* and *access* control for unprivileged processes is governed by
>> +perf_event_paranoid [2]_ setting:
>> +
>> +**-1**:
>> +     Impose no *scope* and *access* restrictions on using PCL performance
>> +     monitoring. Per-user per-cpu perf_event_mlock_kb [2]_ locking limit is
>> +     ignored when allocating memory buffers for storing performance data.
>> +     This is the least secure mode since allowed monitored *scope* is
>> +     maximized and no PCL specific limits are imposed on *resources*
>> +     allocated for performance monitoring.
>> +
>> +**>=0**:
>> +     *scope* includes per-process and system wide performance monitoring
>> +     but excludes raw tracepoints and ftrace function tracepoints monitoring.
>> +     CPU and system events happened when executing either in user or
>> +     in kernel space can be monitored and captured for later analysis.
>> +     Per-user per-cpu perf_event_mlock_kb locking limit is imposed but
>> +     ignored for unprivileged processes with CAP_IPC_LOCK [6]_ capability.
>> +
>> +**>=1**:
>> +     *scope* includes per-process performance monitoring only and excludes
>> +     system wide performance monitoring. CPU and system events happened when
>> +     executing either in user or in kernel space can be monitored and
>> +     captured for later analysis. Per-user per-cpu perf_event_mlock_kb
>> +     locking limit is imposed but ignored for unprivileged processes with
>> +     CAP_IPC_LOCK capability.
>> +
>> +**>=2**:
>> +     *scope* includes per-process performance monitoring only. CPU and system
>> +     events happened when executing in user space only can be monitored and
>> +     captured for later analysis. Per-user per-cpu perf_event_mlock_kb
>> +     locking limit is imposed but ignored for unprivileged processes with
>> +     CAP_IPC_LOCK capability.
>> +
>> +**>=3**:
>> +     Restrict *access* to PCL performance monitoring for unprivileged processes.
>> +     This is the default on Debian and Android [7]_ , [8]_ .
> 
> that ** crud is unreadable.

It can be avoided without missing the sense.

"two asterisks: **text** for strong emphasis (boldface)". 

Thanks,
Alexey

> 
> http://lkml.kernel.org/r/094556ca-ea87-9c4a-2115-600d2833fb2a@darmarit.de
>