Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754582AbcKUQmt (ORCPT ); Mon, 21 Nov 2016 11:42:49 -0500 Received: from mail-it0-f48.google.com ([209.85.214.48]:37728 "EHLO mail-it0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753467AbcKUQmr (ORCPT ); Mon, 21 Nov 2016 11:42:47 -0500 MIME-Version: 1.0 In-Reply-To: References: <147931984418.16460.6639993676886095760.stgit@warthog.procyon.org.uk> <147931990959.16460.3038875071067540418.stgit@warthog.procyon.org.uk> From: Ard Biesheuvel Date: Mon, 21 Nov 2016 16:42:45 +0000 Message-ID: Subject: Re: [PATCH 9/9] MODSIGN: Allow the "db" UEFI variable to be suppressed To: Josh Boyer Cc: David Howells , keyrings@vger.kernel.org, Matthew Garrett , "linux-efi@vger.kernel.org" , "linux-kernel@vger.kernel.org" , linux-security-module Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1092 Lines: 26 On 21 November 2016 at 16:26, Josh Boyer wrote: > On Mon, Nov 21, 2016 at 11:18 AM, Ard Biesheuvel > wrote: >> On 16 November 2016 at 18:11, David Howells wrote: >>> From: Josh Boyer >>> >>> If a user tells shim to not use the certs/hashes in the UEFI db variable >>> for verification purposes, shim will set a UEFI variable called >>> MokIgnoreDB. Have the uefi import code look for this and ignore the db >>> variable if it is found. >>> >> >> Similar concern as in the previous patch: it appears to me that you >> can DoS a machine by setting MokIgnoreDB if, e.g., its modules are >> signed against a cert that resides in db, and shim/mokmanager are not >> being used. > > If shim/mokmanager aren't used, then you can't actually modify > MokIgnoreDB. Again, it requires physical access and a reboot into > mokmanager to actually take effect. > This does the trick as well printf "\x07\x00\x00\x00\x01" > /sys/firmware/efi/efivars/MokIgnoreDB-605dab50-e046-4300-abb6-3dd810dd8b23