Re: Allow automatic kernel taint on unsigned module load to be disabled

From: Ben Hutchings <ben@decadent.org.uk>
To: Matthew Garrett <mjg59@google.com>, Jessica Yu <jeyu@kernel.org>
Cc: linux-kernel@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: Allow automatic kernel taint on unsigned module load to be disabled
Date: Tue, 29 Aug 2017 23:02:02 +0100	[thread overview]
Message-ID: <1504044122.4448.24.camel@decadent.org.uk> (raw)
In-Reply-To: <CACdnJutWdHi5YOG1Mn0vZwTmZyQHyyABeZ0caNn2rJCYehCGhg@mail.gmail.com>

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On Tue, 2017-08-29 at 13:22 -0700, Matthew Garrett wrote:
> > On Tue, Aug 29, 2017 at 10:56 AM, Jessica Yu <jeyu@kernel.org> wrote:
> > I understand what the patch is doing, what I don't yet understand is
> > _why_ you would want to remove the unsigned module taint when
> > CONFIG_MODULE_SIG is enabled. Which distributions are asking for this
> > exactly, and for what use cases? I find it a bit contradictory to have
> > CONFIG_MODULE_SIG enabled and at the same time expect the kernel to
> > behave as if the option wasn't enabled.
> 
> Debian disable CONFIG_MODULE_SIG because of this additional taint
> (I've Cc:ed Ben who made this change).

The current state of affairs is that Debian doesn't have the mechanism
in place to sign modules with a trusted key.  If we were to allow third
parties to add signatures in some way (I think that's what Matthew's
interested in doing) we would have to enabled CONFIG_MODULE_SIG, but
that would cause modules to be tainted by default.

> > I would really prefer not to add extra code to remove what is cosmetic
> > and still has informational/debug value. If the unsigned module taint
> > is for whatever reason that bothersome, why can't distro(s) carry a
> > 2-line patch removing the message and taint for those particular
> > setups where signatures are considered "irrelevant" even with
> > CONFIG_MODULE_SIG=y?
> 
> If it's functionality that distributions want to patch out, it makes
> sense to provide them with a config option rather than forcing them to
> maintain a patch separately.

We could use this in Debian.  It would likely be a temporary stage
until we do our own centralised module signing (or someone implements a
Merkle tree for in-tree modules).

Ben.

-- 
Ben Hutchings
Teamwork is essential - it allows you to blame someone else.

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