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 X-Spam-Level: X-Spam-Status: No, score=-12.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6B144C433B4 for ; Wed, 19 May 2021 14:53:49 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id C945960234 for ; Wed, 19 May 2021 14:53:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C945960234 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:49940 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ljNZz-0000yj-Qg for qemu-devel@archiver.kernel.org; Wed, 19 May 2021 10:53:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34816) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ljNVn-0005cw-GK for qemu-devel@nongnu.org; Wed, 19 May 2021 10:49:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:60662) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ljNVf-0003UJ-Ff for qemu-devel@nongnu.org; Wed, 19 May 2021 10:49:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1621435758; 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:in-reply-to:in-reply-to: references:references; bh=ngzjbfa4dnJ7VCGPENzaTXIurcbEomB7ubIW8xiuOsE=; b=DgQeKnp6oBCq8FaunBkGfTI3nAfyt/jYyx6HwwyxGyM0QdTclomhAnbWjfdaYr7oD6Rc+w uCVvsfGXD2rvq4MsDAYbL8rwEapd+zjMGlFn8TfH6y/j4/aKNp/g8ulLX93L0oiuuNZE9o zDg1ZwCM6a+YsEHXtA41nJhTWETmlmA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-516-15BjGbEbOHmBI-J-vsJSoQ-1; Wed, 19 May 2021 10:49:13 -0400 X-MC-Unique: 15BjGbEbOHmBI-J-vsJSoQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DE35A107ACC7 for ; Wed, 19 May 2021 14:49:12 +0000 (UTC) Received: from redhat.com (ovpn-115-106.ams2.redhat.com [10.36.115.106]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 43F9B19023; Wed, 19 May 2021 14:49:08 +0000 (UTC) Date: Wed, 19 May 2021 15:49:05 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Subject: Re: Automatic module loading (was: [PATCH] qemu-config: load modules when instantiating option groups) Message-ID: References: <20210518131542.2941207-1-pbonzini@redhat.com> <87h7iyoofl.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87h7iyoofl.fsf@dusky.pond.sub.org> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline 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: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.39, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Paolo Bonzini , qemu-devel@nongnu.org, kraxel@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, May 19, 2021 at 03:14:54PM +0200, Markus Armbruster wrote: > Paolo Bonzini writes: > > > Right now the SPICE module is special cased to be loaded when processing > > of the -spice command line option. However, the spice option group > > can also be brought in via -readconfig, in which case the module is > > not loaded. > > > > Add a generic hook to load modules that provide a QemuOpts group, > > and use it for the "spice" and "iscsi" groups. > > > > Fixes: #194 > > Fixes: https://bugs.launchpad.net/qemu/+bug/1910696 > > Signed-off-by: Paolo Bonzini > > What follows is not an objection to this patch. > > I think we have this kind of bugs because we're kind of wobbly on when > to load modules. > > On the one hand, we're trying to load modules only when needed. This is > obviously useful to conserve resources, and to keep the attack surface > small. Some background in > > Message-ID: <20210409064642.ah2tz5vjz2ngfiyo@sirius.home.kraxel.org> > https://lists.gnu.org/archive/html/qemu-devel/2021-04/msg01393.html I'm not convinced by the runtime attack surface argument, because even if QEMU doesn't auto-load, if the attacker has gained enough control over QEMU that they can jump into code that is not otherwise enabled by QEMU config, then they can likely scribble into RAM in a way that triggers dlopen() of any .so on the filesystem, whether a QEMU module or not. IMHO the main benefit of modules is that you can avoid installing everything on disk, and thus avoid pulling in a long chain of deps, and thus get smaller containers, and avoid having to worry about software updates for CVEs in things you're not using. > On the other hand, we're trying to make modules transparent to > management applications, i.e. QEMU looks the same whether something was > compiled as a loadable module or linked into QEMU itself. See > > Message-ID: > https://lists.gnu.org/archive/html/qemu-devel/2021-04/msg01450.html > > I'm afraid we sort of fail at both. > > Transparency to management applications requires us to load modules on > QOM introspection already. Yes, and bugs in the latter have already caused mis-behavior in libvirt. > Example: to answer "show me all QOM types", we need to load all modules > that could possibly register QOM types. As long as module code can do > whatever it wants, that means loading all of them. > > Example: to answer "show me QOM type FOO", where FOO is currently > unknown, we need to load all modules that could possible register QOM > type FOO. Again, that means loading all of them. > > We don't actually do this. Instead, we hardcode a map from type name to > module name[*], so we don't have to load them all, and we actually load > the module specified by this map only sometimes, namely when we call > module_object_class_by_name() instead of object_class_by_name(). I > can't discern rules when to call which one. Wobbly. > > Things other than QOM might be affected, too. > > QAPI introspection is not: the value of query-qmp-schema is fixed at > compile-time, and *how* something is compiled (loadable module > vs. linked into QEMU itself) does not affect it. > > I'd like us to develop a clearer understanding when exactly modules are > to be loaded. Agreed, we need much better defined behaviour here. 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 :|