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Date: Mon, 3 Dec 2018 12:42:09 +0300
From: Alexey Budankov <>
To: Jonathan Corbet <>, Peter Zijlstra <>
Cc: Thomas Gleixner <>, Kees Cook <>,
 Jann Horn <>, Ingo Molnar <>,
 Andi Kleen <>,
 Alexander Shishkin <>,
 Jiri Olsa <>, Arnaldo Carvalho de Melo <>,
 Mark Rutland <>, Tvrtko Ursulin <>,
 linux-kernel <>,
 "" <>,
 "" <>
Subject: Re: [PATCH v4 1/2] Documentation/admin-guide: introduce
 perf-security.rst file

Hi Peter,

On 27.11.2018 22:13, Alexey Budankov wrote:
> On 27.11.2018 21:11, Jonathan Corbet wrote:
>> On Tue, 27 Nov 2018 11:15:37 +0300
>> Alexey Budankov <> wrote:
>>> +To perform security checks, the Linux implementation splits processes into two
>>> +categories [6]_ : a) privileged processes (whose effective user ID is 0, referred
>>> +to as superuser or root), and b) unprivileged processes (whose effective UID is
>>> +nonzero). Privileged processes bypass all kernel security permission checks so
>>> +perf_events performance monitoring is fully available to privileged processes
>>> +without access, scope and resource restrictions.
>>> +
>>> +Unprivileged processes are subject to a full security permission check based on
>>> +the process's credentials [5]_ (usually: effective UID, effective GID, and
>>> +supplementary group list).
>>> +
>>> +Linux divides the privileges traditionally associated with superuser into
>>> +distinct units, known as capabilities [6]_ , which can be independently enabled
>>> +and disabled on per-thread basis for processes and files of unprivileged users.
>>> +
>>> +Unprivileged processes with enabled CAP_SYS_ADMIN capability are treated as
>>> +privileged processes with respect to perf_events performance monitoring and
>>> +bypass *scope* permissions checks in the kernel.
>>> +
>>> +Unprivileged processes using perf_events system call API is also subject for
>>> +PTRACE_MODE_READ_REALCREDS ptrace access mode check [7]_ , whose outcome
>>> +determines whether monitoring is permitted. So unprivileged processes provided
>>> +with CAP_SYS_PTRACE capability are effectively permitted to pass the check.
>> It's good to have more information here.  I could certainly quibble
>> further with things - a process with CAP_SYS_ADMIN is not "unprivileged"!
>> - but I don't want to stand in the way of this any further.  I *would*
>> still like to see an ack from the perf world, though.
> Thanks for meaningful comments! Looking forward to ack from perf world.

May I ask you to review v4 of the patches? 
Your comments on v1 have been addressed in there.


>> With regard to Kees's comment on merging the two patches; I would probably
>> add the new document to index.rst in the same patch, but it doesn't matter
>> that much.  Not worth redoing the patch just for that.
> Thanks,
> Alexey
>> jon

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