From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9D4BCC05027 for ; Wed, 1 Feb 2023 15:15:56 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pNEpF-0005Yi-C4; Wed, 01 Feb 2023 10:15:05 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pNEpC-0005XZ-Py for qemu-devel@nongnu.org; Wed, 01 Feb 2023 10:15:02 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pNEpA-0003vo-00 for qemu-devel@nongnu.org; Wed, 01 Feb 2023 10:15:02 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675264498; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1ozcLz0H0d96wx1I3zsbreUXm6C/PzLk3JxmLnv3nbw=; b=fpC5t68vu20A/uolKLqO9VcCBZPQZPKcvgS8r6APfW+9RwxRSE35MTq2+UAS1vhKw6doVD nNLtJMSOAVZ2CDuO93Dvr9Cqd+MyVecJMfqONdMep++6mG0rZkC+eSZtzjYnQDHOsL4vxr f62ihTt9m78SijyWREwpCxvy1Y6JLJw= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-266-EqxjND0NMqejvO2UU70jig-1; Wed, 01 Feb 2023 10:14:57 -0500 X-MC-Unique: EqxjND0NMqejvO2UU70jig-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2E3E03C10EC2; Wed, 1 Feb 2023 15:14:57 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.62]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 237A6404BEC0; Wed, 1 Feb 2023 15:14:55 +0000 (UTC) Date: Wed, 1 Feb 2023 15:14:53 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: James Bottomley Cc: qemu-devel@nongnu.org, Gerd Hoffmann , DOV MURIK , "Jason A. Donenfeld" Subject: Re: [PATCH] x86: fix q35 kernel measurements broken due to rng seeding Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Feb 01, 2023 at 09:56:35AM -0500, James Bottomley wrote: > On Wed, 2023-02-01 at 14:35 +0000, Daniel P. Berrangé wrote: > > On Wed, Feb 01, 2023 at 08:57:10AM -0500, James Bottomley wrote: > > > The origin commit for rng seeding 67f7e426e5 ("hw/i386: pass RNG > > > seed > > > via setup_data entry") modifies the kernel image file to append a > > > random seed.  Obviously this makes the hash of the kernel file > > > non-deterministic and so breaks both measured and some signed > > > boots. > > > > I recall raising that at the time > > > >   https://lists.gnu.org/archive/html/qemu-devel/2022-08/msg00710.html > > > > and Jason pointed me to a followup which I tested and believe > > fixed it for SEV: > > > >   https://lists.gnu.org/archive/html/qemu-devel/2022-08/msg00601.html > > > > but it doesn't look like that second patch ever merged. We went > > through so many patches I think it probably got obsoleted by > > something else, and no one rechecked SEV again. > > The kernel file problem is a pretty huge one. OVMF lays it down on an > internal file system and without the second patch, it now contains > random junk at the end. Anything that hashes the whole file (which > includes not only the measured direct boot but also grub signatures and > probably other bootloader signing mechanisms) will have an issue. > > > > The commit notes it's only for non-EFI (because EFI has a different > > > RNG seeding mechanism) so, since there are no non-EFI q35 systems, > > > this should be disabled for the whole of the q35 machine type to > > > bring back deterministic kernel file hashes. > > > > SeaBIOS is the default firmware for both q35 and i440fx. The > > majority of systems using q35 will be non-EFI today, and that > > is what the random seed was intended to address. I don't think > > we can just disable this for the whole of q35. > > > > When you say it breaks measured / signed boots, I presume you > > are specifically referring to SEV kernel hashes measurements ? > > Or is there a more general problem to solve ? > > No it generally breaks measured/signed boots because it adds random > junk to the kernel file. The second patch will fix this if you apply > it because setup data isn't measured or signed (yet ... however see the > linux-coco debate about how it should be). BTW, I can't find a reference now, but I recall being told that when using -kernel, OVMF won't enforce SecureBoot. ie it'll do the checks but ignore any failure and carry on. It should still be reflected in the vTPM measurements though. > I also note there was a v3 of the patch and considerable discussion > saying it couldn't work: > > https://lore.kernel.org/qemu-devel/20220804230411.17720-1-Jason@zx2c4.com/ > > Which is likely why it never went in ... although the discussion does > seem to resolve towards the end. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|