linux-kernel - Re: Firmware signing -- Re: [PATCH 00/27] security, efi: Add kernel lockdown

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Date:   Tue, 14 Nov 2017 08:17:14 -0500
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        "AKASHI, Takahiro" <takahiro.akashi@...aro.org>,
        Jan Blunck <jblunck@...radead.org>,
        Julia Lawall <julia.lawall@...6.fr>,
        Marcus Meissner <meissner@...e.de>, Gary Lin <GLin@...e.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Matthew Garrett <mjg59@...gle.com>
Subject: Re: Firmware signing -- Re: [PATCH 00/27] security, efi: Add kernel
 lockdown

On Tue, 2017-11-14 at 13:38 +0100, Greg Kroah-Hartman wrote:
> On Tue, Nov 14, 2017 at 07:21:38AM -0500, Mimi Zohar wrote:
> > On Mon, 2017-11-13 at 14:09 -0800, Linus Torvalds wrote:
> > > On Mon, Nov 13, 2017 at 1:44 PM, David Howells <dhowells@...hat.com> wrote:
> > > >
> > > > Whilst that may be true, we either have to check signatures on every bit of
> > > > firmware that the appropriate driver doesn't say is meant to be signed or not
> > > > bother.
> > > 
> > > I vote for "not bother".
> > > 
> > > Seriously, if you have firmware in /lib/firmware, and you don't trust
> > > it, what the hell are you doing?
> > 
> > I might "trust" the files in /lib/firmware, but I also want to make
> > sure that they haven't changed.  File signatures provide file
> > provenance and integrity guarantees.
> 
> Then "verify" them with signatures that you generate yourself.  Like
> dm-verify does for the partition that you put the firmware on.

The discussion, here, is in the context of the "lockdown" patch set,
without IMA-appraisal configured.  Kernel modules and the kexec kernel
image require file signatures in lockdown mode.  An equivalent method
of requiring file signatures for firmware (without IMA-appraisal) does
not exist.

I posted the patch [RFC PATCH v2] "fw_lockdown: new micro LSM module
to prevent loading unsigned firmware".  The patch and discussion can
be found here - (https://lkml.org/lkml/2017/11/13/217).

Mimi