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

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Message-ID: <20181126132833.5302688b@lwn.net>
Date:   Mon, 26 Nov 2018 13:28:33 -0700
From:   Jonathan Corbet <corbet@....net>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
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

On Mon, 26 Nov 2018 11:57:21 +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.

I don't really like the idea of adding a document that we know doesn't
really describe how the security decision is made.  Even a one-line
parenthetical saying that things are more complicated and giving a pointer
to a place to look for details would help, IMO.

Either way, I can merge this, but I'd like to have an ack from the perf
folks first.

Thanks,

jon