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 0C8E7C83F25 for ; Mon, 21 Jul 2025 15:29:13 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1udsRP-0008Iu-4u; Mon, 21 Jul 2025 11:28:35 -0400 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 1udsRM-0008GB-Cn for qemu-devel@nongnu.org; Mon, 21 Jul 2025 11:28:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1udsRK-00088c-7V for qemu-devel@nongnu.org; Mon, 21 Jul 2025 11:28:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1753111706; 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=AIYOG6eMK68bbz8MtSCsQjXM3HKWyNXqF8tskWvW3xk=; b=bu03ERs55RUkQUTC0sOZwqrOQx6bmqUsI5w4XJ708Dyz7rojhWGkgHoPq4putVw2Qt4a2+ cf2BgC2G3j4kfeuClZClrODy3kLgdVqgj6bVULRxiMUCzV58P0mDxUshE5KuKnFHn9PqX8 Nf4hGihgJJBgal4NtH0T30goZjl1JAE= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-519-YmWtZOfWO6S2QZyubJjWtQ-1; Mon, 21 Jul 2025 11:28:23 -0400 X-MC-Unique: YmWtZOfWO6S2QZyubJjWtQ-1 X-Mimecast-MFC-AGG-ID: YmWtZOfWO6S2QZyubJjWtQ_1753111702 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D8F031800365; Mon, 21 Jul 2025 15:28:21 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.213]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B407519560AD; Mon, 21 Jul 2025 15:28:19 +0000 (UTC) Date: Mon, 21 Jul 2025 16:28:16 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Fabiano Rosas Cc: qemu-devel@nongnu.org, Paolo Bonzini , Peter Xu , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Subject: Re: [PATCH 0/4] migration: workaround GNUTLS live migration crashes Message-ID: References: <20250718150514.2635338-1-berrange@redhat.com> <871pq9lhiu.fsf@suse.de> <87y0shk238.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87y0shk238.fsf@suse.de> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -2 X-Spam_score: -0.3 X-Spam_bar: / X-Spam_report: (-0.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.926, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, GUARANTEED_100_PERCENT=2.699, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no 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 Mon, Jul 21, 2025 at 12:14:51PM -0300, Fabiano Rosas wrote: > Daniel P. Berrangé writes: > > > On Mon, Jul 21, 2025 at 11:56:09AM -0300, Fabiano Rosas wrote: > >> Daniel P. Berrangé writes: > >> > >> > TL:DR: GNUTLS is liable to crash QEMU when live migration is run > >> > with TLS enabled and a return path channel is present, if approx > >> > 64 GB of data is transferred. This is easily triggered in a 16 GB > >> > VM with 4 CPUs, by running 'stress-ng --vm 4 --vm-bytes 80%' to > >> > prevent convergance until 64 GB of RAM has been copied. Then > >> > triggering post-copy switchover, or removing the stress workload > >> > to allow completion, will crash it. > >> > > >> > The only live migration scenario that should avoid this danger > >> > is multifd, since the high volume data transfers are handled in > >> > dedicated TCP connections which are unidirectional. The main > >> > bi-directionl TCP connection is only for co-ordination purposes > >> > > >> > This patch implements a workaround that will prevent future QEMU > >> > versions from triggering the crash. > >> > > >> > The only way to avoid the crash with *existing* running QEMU > >> > processes is to change the TLS cipher priority string to avoid > >> > use of AES with TLS 1.3. This can be done with the 'priority' > >> > field in the 'tls-creds-x509' object.eg > >> > > >> > -object tls-creds-x509,id=tls0,priority=NORMAL:-AES-256-GCM:-AES-128-GCM:-AES-128-CCM > >> > > >> > which should force the use of CHACHA20-POLY1305 which does not > >> > require TLS re-keying after 16 million sent records (64 GB of > >> > migration data). > >> > > >> > https://gitlab.com/qemu-project/qemu/-/issues/1937 > >> > > >> > On RHEL/Fedora distros you can also use the system wide crypto > >> > priorities to override this from the migration *target* host > >> > by creating /etc/crypto-policies/local.d/gnutls-qemu.config > >> > containing > >> > > >> > QEMU=NONE:+ECDHE-RSA:+ECDHE-ECDSA:+RSA:+DHE-RSA:+GROUP-X25519:+GROUP-X448:+GROUP-SECP256R1:+GROUP-SECP384R1:+GROUP-SECP521R1:+GROUP-FF > >> > > >> > and running 'update-crypto-policies'. I recommend the QEMU > >> > level 'tls-creds-x509' workaround though, which new libvirt > >> > patches can soon do: > >> > > >> > https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/LX5KMIUFZSP5DPUXKJDFYBZI5TIE3E5N/ > >> > > >> > Daniel P. Berrangé (4): > >> > crypto: implement workaround for GNUTLS thread safety problems > >> > io: add support for activating TLS thread safety workaround > >> > migration: activate TLS thread safety workaround > >> > crypto: add tracing & warning about GNUTLS countermeasures > >> > > >> > crypto/tlssession.c | 99 +++++++++++++++++++++++++++++++++-- > >> > crypto/trace-events | 2 + > >> > include/crypto/tlssession.h | 14 +++++ > >> > include/io/channel.h | 1 + > >> > io/channel-tls.c | 5 ++ > >> > meson.build | 9 ++++ > >> > meson_options.txt | 2 + > >> > migration/tls.c | 9 ++++ > >> > scripts/meson-buildoptions.sh | 5 ++ > >> > 9 files changed, 143 insertions(+), 3 deletions(-) > >> > >> Hi, thank you for getting to the bottom of this. > >> > >> Do you think it would be too cumbersome to add a test for this > >> somewhere? So we don't regress the workaround but also so the test tells > >> us whether GNUTLS is fixed. > > > > The reproducer scenario is very expensive. I'm doing it with a 16 GB RAM > > guest, with 4 CPUs, running 'stress-ng' guest workload. With that, it > > takes between 10-20 minutes before live migration gets GNUTLS into the > > potentially broken state, and the failure is not 100% guaranteed at > > that point. > > > > Makes sense. Thanks. > > Will you take the series or should I? I presume you've already got another migration pull request planned, so feel free to add this 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 :|