linux-kernel - Re: [PATCH v2 1/2] Documentation/admin-guide: introduce perf-security.rst file

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Message-ID: <02dbd6dc-86b5-2307-4122-b716c51b9eaa@linux.intel.com>
Date:   Mon, 26 Nov 2018 11:57:21 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jonathan Corbet <corbet@....net>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        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" 
        <kernel-hardening@...ts.openwall.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] Documentation/admin-guide: introduce
 perf-security.rst file

Hello Jon,

On 25.11.2018 22:47, Jonathan Corbet wrote:
> On Wed, 21 Nov 2018 12:14:14 +0300
> Alexey Budankov <alexey.budankov@...ux.intel.com> wrote:
> 
>> +For the purpose of performing security checks 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).
> 
> Is that really what's going on here?  If I understand things correctly,
> it's looking for CAP_SYS_PTRACE rather than a specific UID; am I missing
> something here?

You are right regarding CAP_SYS_PTRACE but this capability is not the only 
one which is used by perf_events for security checks, so the capabilities 
clarification is kept aside of these patches, because patches initial intention 
is to clarify security specifics of sysctl_perf_even_paranoid settings.

I agree that the document can be extended with details clarifying capabilities 
used by perf_events for security checks.

> 
> (Also, you would want "*the* Linux implementation" in the first sentence
> above).

Accepted.

> 
> One other thing:
> 
>> +(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.
> 
> Could I ask for a slight toning down of the markup here?  There's a lot of
> *emphasis* here that isn't really needed and tends to get in the way.

Accepted.

Thanks,
Alexey

> 
> Thanks,
> 
> jon
>