linux-kernel - Re: [kernel-hardening] [PATCH v4 next 0/3] modules: automatic module loading restrictions

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Date:   Tue, 23 May 2017 11:36:36 -0700
From:   Kees Cook <keescook@...gle.com>
To:     Solar Designer <solar@...nwall.com>
Cc:     Djalal Harouni <tixxdz@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rusty Russell <rusty@...tcorp.com.au>,
        "Serge E. Hallyn" <serge@...lyn.com>, Jessica Yu <jeyu@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        James Morris <james.l.morris@...cle.com>,
        Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Ingo Molnar <mingo@...nel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Dongsu Park <dpark@...teo.net>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Jonathan Corbet <corbet@....net>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Zendyani <zendyani@...il.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>
Subject: Re: [kernel-hardening] [PATCH v4 next 0/3] modules: automatic module
 loading restrictions

On Tue, May 23, 2017 at 12:48 AM, Solar Designer <solar@...nwall.com> wrote:
> For modules_autoload_mode=2, we already seem to have the equivalent of
> modprobe=/bin/true (or does it differ subtly, maybe in return values?),
> which I already use at startup on a GPU box like this (preloading
> modules so that the OpenCL backends wouldn't need the autoloading):
>
> nvidia-smi
> nvidia-modprobe -u -c=0
> #modprobe nvidia_uvm
> #modprobe fglrx
>
> sysctl -w kernel.modprobe=/bin/true
> sysctl -w kernel.hotplug=/bin/true
>
> but it's good to also have this supported more explicitly and more
> consistently through modules_autoload_mode=2 while we're at it.  So I
> support having this mode as well.  I just question the need to have it
> non-resettable.

I agree it's useful to have the explicit =2 state just to avoid
confusion when more systems start implementing
CONFIG_STATIC_USERMODEHELPER and kernel.modprobe becomes read-only
(though the userspace implementation may allow for some way to disable
it, etc). I just like avoiding the upcall to modprobe at all.

-Kees

-- 
Kees Cook
Pixel Security