From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752992AbdKIBpW (ORCPT ); Wed, 8 Nov 2017 20:45:22 -0500 Received: from mail-pg0-f45.google.com ([74.125.83.45]:54466 "EHLO mail-pg0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752697AbdKIBpU (ORCPT ); Wed, 8 Nov 2017 20:45:20 -0500 X-Google-Smtp-Source: ABhQp+T9E5dvXtc1ihstToNYuSQPFBzaSBR/QmsuHi5HOiuZV5zojCDj4F+Uai74bcGlLTTOEfbMFg== Date: Thu, 9 Nov 2017 10:48:43 +0900 From: "AKASHI, Takahiro" To: "Luis R. Rodriguez" Cc: Greg Kroah-Hartman , Linus Torvalds , Mimi Zohar , Jan Blunck , Julia Lawall , David Howells , Marcus Meissner , Gary Lin , linux-security-module@vger.kernel.org, gnomes@lxorguk.ukuu.org.uk, linux-efi , linux-kernel@vger.kernel.org, Matthew Garrett Subject: Re: Firmware signing -- Re: [PATCH 00/27] security, efi: Add kernel lockdown Message-ID: <20171109014841.GF7859@linaro.org> Mail-Followup-To: "AKASHI, Takahiro" , "Luis R. Rodriguez" , Greg Kroah-Hartman , Linus Torvalds , Mimi Zohar , Jan Blunck , Julia Lawall , David Howells , Marcus Meissner , Gary Lin , linux-security-module@vger.kernel.org, gnomes@lxorguk.ukuu.org.uk, linux-efi , linux-kernel@vger.kernel.org, Matthew Garrett References: <1509660086.3416.15.camel@linux.vnet.ibm.com> <150842463163.7923.11081723749106843698.stgit@warthog.procyon.org.uk> <14219.1509660259@warthog.procyon.org.uk> <1509660641.3416.24.camel@linux.vnet.ibm.com> <20171107230700.GJ22894@wotan.suse.de> <20171108061551.GD7859@linaro.org> <20171108194626.GQ22894@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20171108194626.GQ22894@wotan.suse.de> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 08, 2017 at 08:46:26PM +0100, Luis R. Rodriguez wrote: > On Wed, Nov 08, 2017 at 03:15:54PM +0900, AKASHI, Takahiro wrote: > > Luis, > > > > Thank you for this heads-up. > > > > On Wed, Nov 08, 2017 at 12:07:00AM +0100, Luis R. Rodriguez wrote: > > > On Thu, Nov 02, 2017 at 06:10:41PM -0400, Mimi Zohar wrote: > > > > On Thu, 2017-11-02 at 22:04 +0000, David Howells wrote: > > > > > Mimi Zohar wrote: > > > > > > > > > > > > Only validly signed device firmware may be loaded. > > > > > > > > > > > > fw_get_filesystem_firmware() calls kernel_read_file_from_path() to > > > > > > read the firmware, which calls into the security hooks. Is there > > > > > > another place that validates the firmware signatures.  I'm not seeing > > > > > > which patch requires firmware to be signed? > > > > > > > > > > Luis has a set of patches for this. However, I'm not sure if that's going > > > > > anywhere at the moment. Possibly I should remove this from the manpage for > > > > > the moment. > > > > > > Remove it for now. The state of of affairs for firmware signing is complex given > > > that we first wanted to address how to properly grow the API without making > > > the API worse. This in and of itself was an effort, and that effort also > > > evaluated two different development paradigms: > > > > > > o functional API > > > o data driven API > > > > > > I only recently was convinced that functional API should be used, even for > > > commonly used exported symbols, > > > > Are you? > > Yes, this stemmed from the fact that even system calls can be abused through > data driven APIs, and that long term a functional API at least can make > evolutions much easier to review and bisect. > > That said this is all based on *empirical hearsay*, and no formal observations. > But the ease to more easily bisect long term is enough for me to consider this > for the firmware API given subtle regressions have been a long standing pain > on the firmware API and I would not want to make the process of bisecting > any harder. > > If anyone *does* have actual efforts which compares and contrasts both, I'd > love to get them, to further back my current position, but as-is I'm already > sold on functional API driven interface. > > > I haven't answered Linus' question, but my concern about functional APIs, > > as far as firmware signing goes, is that we have no way to _enforce_ > > firmware signing to existing (i.e. verification-unaware) drivers if we need > > an explicit call of a function, say, verify_firmware(). > > Your concern seems to be that a functional driven API for firmware signing would > implicate having to support verify_firmware() for drivers which *cannot* get > signed firmware verified, is that correct? > > IMHO that should just fail then, ie, a "locked down" kernel should not want to > *pass* a firmware signature if such thing could not be done. > > Its no different than trying to verify a signed module on a "locked down" for > which it has no signature. > > 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. If you allow me to bring in yet another function, say request_firmware_signable(), which should be used in place of (a) for all verification-aware drivers, that would be fine. In this case, all the invocation of request_firmware() in legacy code could be forced to fail in locked-down kernel. But I think that "signable" should be allowed to be combined with other features of request_firmware variants like _(no)wait or _direct. -Takahiro AKASHI > > > > and as such I've been going back and slowly > > > grooming the firmware API with small atomic changes to first clean up the > > > complex flag mess we have. > > > > > > Since I'm busy with that Takahiro AKASHI has taken up firmware singing effort > > > but this will depend on the above small cleanup to be done first. I was busy > > > with addressing existing bugs on the firmware API for a while, then company > > > travel / conferences so was not able to address this, but I'm back now and > > > I believe I should be able to tackle the cleanup now. > > > > Good to hear. > > > > > Only after this is merged can we expect a final respin of the firmware signing > > > effort. > > > > > > > Or reflect that IMA-appraisal, if enabled, will enforce firmware being > > > > validly signed. > > > > > > But FWICT lockdown is a built-in kernel thingy, unless lockdown implies IMA > > > it would not be the place to refer to it. > > > > I think that the situation is the same as in module signing. > > But by definition a "locked down" kernel will enforce module signing, and it > would seem logical that if modules signing is enforced, eventually a statement > about firmware signing can be added, as it relates to a kernel enforcement > effort, not a kernel-userpace framework such as IMA. > > Luis > > > -Takahiro AKASHI > > > > > It seems the documentation was proposed to help users if an error was caught. > > > That error should cover only what is being addressed in code on the kernel. > > > > > > Luis > > > > -- > Luis Rodriguez, SUSE LINUX GmbH > Maxfeldstrasse 5; D-90409 Nuernberg