From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mimi Zohar <zohar-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
Subject: Re: Firmware signing -- Re: [PATCH 00/27] security, efi: Add kernel
 lockdown
Date: Fri, 10 Nov 2017 08:45:06 -0500
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To: "Luis R. Rodriguez" <mcgrof-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, "AKASHI, Takahiro" <takahiro.akashi-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Cc: Greg Kroah-Hartman <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>, Jan Blunck <jblunck-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Julia Lawall <julia.lawall-L2FTfq7BK8M@public.gmane.org>, David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Marcus Meissner <meissner-l3A5Bk7waGM@public.gmane.org>, Gary Lin <GLin-IBi9RG/b67k@public.gmane.org>, Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>, James Bottomley <James.Bottomley-JuX6DAaQMKPCXq6kfMZ53/egYHeGw8Jk@public.gmane.org>, Peter Jones <pjones-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, linux-security-module-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, gnomes-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org, linux-efi <linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Matthew Garrett <mjg59-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
List-Id: linux-efi@vger.kernel.org

On Fri, 2017-11-10 at 02:46 +0100, Luis R. Rodriguez wrote:
> On Thu, Nov 09, 2017 at 10:48:43AM +0900, AKASHI, Takahiro wrote:
> > On Wed, Nov 08, 2017 at 08:46:26PM +0100, Luis R. Rodriguez wrote:
> > > But perhaps I'm not understanding the issue well, let me know.
> > 
> > My point is quite simple:
> > my_deviceA_init() {
> >         err = request_firmware(&fw, "deviceA"); <--- (a)
> >         if (err)
> >                 goto err_request;
> > 
> >         err = verify_firmware(fw);  <--- (b)
> >         if (err)
> >                 goto err_verify;
> > 
> >         load_fw_to_deviceA(fw);     <--- (c)
> >         ...
> > }
> > 
> > As legacy device drivers does not have (b), there is no chance to
> > prevent loading a firmware at (c) for locked-down kernel.
> 
> Ah, I think your example requires another piece of code to make it clearer.
> Here is an example legacy driver:
> 
> my_legacy_deviceB_init() {
>         err = request_firmware(&fw, "deviceB"); <--- (a)
>         if (err)
>                 goto err_request;
> 
>         load_fw_to_deviceA(fw);     <--- (c)
>         ...
> }
> 
> There is no verify_firmware() call here, and as such the approach Linus
> suggested a while ago cannot possibly fail on a "locked down kernel", unless
> *very* legacy API call gets a verify_firmware() sprinkled.
> 
> One sensible thing to say here is then that all request_firmware() calls should
> just fail on a "locked down kernel", however if this were true then even calls
> which *did* issue a subsequent verify_firmware() would fail earlier therefore
> making verify_firmware() pointless on new drivers.

As long as these "*very* legacy API calls", are calling
kernel_read_file_from_path() to read the firmware, there shouldn't be
a problem.

Mimi