From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751751AbeCNOTb (ORCPT ); Wed, 14 Mar 2018 10:19:31 -0400 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:51986 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751682AbeCNOT3 (ORCPT ); Wed, 14 Mar 2018 10:19:29 -0400 Message-ID: <1521037165.4508.13.camel@HansenPartnership.com> Subject: Re: [PATCH 4/5] MODSIGN: checking the blacklisted hash before loading a kernel module From: James Bottomley To: joeyli Cc: "Lee, Chun-Yi" , David Howells , linux-fs@vger.kernel.org, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, Josh Boyer Date: Wed, 14 Mar 2018 07:19:25 -0700 In-Reply-To: <20180314060803.GD19718@linux-l9pv.suse> References: <20180313103803.13388-1-jlee@suse.com> <20180313103803.13388-5-jlee@suse.com> <1520961515.5360.19.camel@HansenPartnership.com> <20180314060803.GD19718@linux-l9pv.suse> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.20.5 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2018-03-14 at 14:08 +0800, joeyli wrote: > On Tue, Mar 13, 2018 at 10:18:35AM -0700, James Bottomley wrote: > > > > On Tue, 2018-03-13 at 18:38 +0800, Lee, Chun-Yi wrote: > > > > > > This patch adds the logic for checking the kernel module's hash > > > base on blacklist. The hash must be generated by sha256 and > > > enrolled > > > to dbx/mokx. > > > > > > For example: > > > sha256sum sample.ko > > > mokutil --mokx --import-hash $HASH_RESULT > > > > > > Whether the signature on ko file is stripped or not, the hash can > > > be > > > compared by kernel. > > > > What's the use case for this?  We're already in trouble from the > > ODMs for the size of dbx and its consumption of the extremely > > limited variable space, so do we really have a use case for adding > > module blacklist hashes to the UEFI variables given the space > > constraints (as in one we can't do any other way)? > > > > The dbx is a authenticated variable that it can only be updated by > manufacturer. The mokx gives a flexible way for distro to revoke a > key or a signed module. Then we don't need to touch shim or bother > manufacturer to deliver new db. Currently it doesn't have real use > case yet.  > > I knew that the NVRAM has limited space. But distro needs a backup > solution for emergency. I wasn't asking why the variable, I was asking why the mechanism. OK, let me try to ask the question in a different way: Why would the distribution need to blacklist a module in this way?  For the distro to execute the script to add this blacklist, means the system is getting automated or manual updates ... can't those updates just remove the module? The point is that module sha sums are pretty ephemeral in our model (they change with every kernel), so it seems to be a mismatch to place them in a permanent blacklist, particularly when we have very limited space for that list. James