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

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Date:   Mon, 13 Nov 2017 18:42:50 +0100
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     "AKASHI, Takahiro" <takahiro.akashi@...aro.org>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Blunck <jblunck@...radead.org>,
        Julia Lawall <julia.lawall@...6.fr>,
        David Howells <dhowells@...hat.com>,
        Marcus Meissner <meissner@...e.de>, Gary Lin <GLin@...e.com>,
        linux-security-module@...r.kernel.org,
        linux-efi <linux-efi@...r.kernel.org>,
        linux-kernel@...r.kernel.org, Matthew Garrett <mjg59@...gle.com>
Subject: Re: Firmware signing -- Re: [PATCH 00/27] security, efi: Add kernel
 lockdown

On Sat, Nov 11, 2017 at 02:32:40AM +0000, Alan Cox wrote:
> > My assumption here is:
> > 1) there are some less important and so security-insensitive firmwares,
> >    by which I mean that such firmwares won't be expected to be signed in
> >    terms of vulnerability or integrity.
> >    (I can't give you examples though.)
> > 2) firmware's signature will be presented separately from the firmware
> >    blob itself. Say, "firmware.bin.p7s" for "firmware.bin"
> 
> For x86 at least any firmware on any system modern enough to support
> 'secure' boot should already be signed. The only major exception is
> likely to be for things like random USB widgets.

Alan, the firmware being considered here is /lib/firmware firmware, which
is not signed today. Its unclear to me how you mean that /lib/firmware files
are already signed or verified today.

> The other usual exception is FPGAs, but since the point of an FPGA is
> usually the fact it *can* be reprogrammed it's not clear that signing
> FPGA firmware makes sense unless it is designed to be fixed function.

Agreed that we may end up with exemptions where we purposely cannot
get signed firmware for, or where for certain drivers this makes no
sense.

  Luis