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=-2.2 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 1A1E7C3A5A2 for ; Fri, 23 Aug 2019 14:55:09 +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 E85D322CE3 for ; Fri, 23 Aug 2019 14:55:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E85D322CE3 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]:57398 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i1Ay3-0006MX-Ld for qemu-devel@archiver.kernel.org; Fri, 23 Aug 2019 10:55:07 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:52182) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i1AkT-0007yN-5l for qemu-devel@nongnu.org; Fri, 23 Aug 2019 10:41:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i1AkR-0008HN-Lt for qemu-devel@nongnu.org; Fri, 23 Aug 2019 10:41:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37456) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i1AkR-0008EZ-CH for qemu-devel@nongnu.org; Fri, 23 Aug 2019 10:41:03 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C6452302C06C; Fri, 23 Aug 2019 14:41:01 +0000 (UTC) Received: from redhat.com (ovpn-112-60.ams2.redhat.com [10.36.112.60]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 19C8E5D6B2; Fri, 23 Aug 2019 14:40:55 +0000 (UTC) Date: Fri, 23 Aug 2019 15:40:52 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Dr. David Alan Gilbert" Message-ID: <20190823144052.GL9654@redhat.com> References: <20190808150325.21939-1-marcandre.lureau@redhat.com> <20190823112053.GE9654@redhat.com> <20190823114157.GG9654@redhat.com> <20190823130014.GG2784@work-vm> <20190823140948.GI2784@work-vm> <20190823142054.GK9654@redhat.com> <20190823142602.GJ2784@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190823142602.GJ2784@work-vm> User-Agent: Mutt/1.12.0 (2019-05-25) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Fri, 23 Aug 2019 14:41:01 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v2 0/2] Add dbus-vmstate 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: Laurent Vivier , Thomas Huth , Juan Quintela , qemu-devel , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Stefan Hajnoczi , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Aug 23, 2019 at 03:26:02PM +0100, Dr. David Alan Gilbert wrote: > * Daniel P. Berrang=C3=A9 (berrange@redhat.com) wrote: > > On Fri, Aug 23, 2019 at 03:09:48PM +0100, Dr. David Alan Gilbert wrot= e: > > > * Marc-Andr=C3=A9 Lureau (marcandre.lureau@gmail.com) wrote: > > > > Hi > > > >=20 > > > > On Fri, Aug 23, 2019 at 5:00 PM Dr. David Alan Gilbert > > > > wrote: > > > > > > > > > > * Daniel P. Berrang=C3=A9 (berrange@redhat.com) wrote: > > > > > > > > > > > > > > > > > > > > > This means QEMU still has to iterate over every single client > > > > > > on the bus to identify them. If you're doing that, there's > > > > > > no point in owning a well known service at all. Just iterate > > > > > > over the unique bus names and look for the exported object > > > > > > path /org/qemu/VMState > > > > > > > > > > > > > > > > Not knowing anything about DBus security, I want to ask how do > > > > > we handle security here? > > > >=20 > > > > First of all, we are talking about cooperative processes, and hav= ing a > > > > specific bus for each qemu instance. So some amount of security/t= rust > > > > is already assumed. > > >=20 > > > Some but we need to keep it as limited as possible; for example two > > > reasons for having separate processes both come down to security: > > >=20 > > > a) vtpm - however screwy the qemu is, you can never get to the ke= ys in > > > the vtpm > >=20 > > Processes connected to dbus can only call the DBus APIs that vtpm > > actually exports. The vtpm should simply *not* export a DBus > > API that allows anything to fetch the keys. > >=20 > > If it did want to export APIs for fetching keys, then we would > > have to ensure suitable dbus /selinux policy was created to > > prevent unwarranted access. >=20 > This was really just one example of where the security/trust isn't > assumed; however a more concrete case is migration of a vtpm, and even > though it's probably encrypted blob you still don't want some other > device to grab the migration data - or to say reinitialise the vtpm. That can be dealt with by the dbus security policies, provided you either run the vtpm as a different user ID from the other untrustworthy helpers, or use a different selinux context for vtpm. You can then express that only the user that QEMU is running under can talk to vtpm over dbus. Where I think you could have problems is if you needed finer grainer control with selinux. eg if vstpm exports 2 different services, you can't allow access to one service, but forbid access to the other service. > > > b) virtio-gpu, loads of complex GPU code that can't break the mai= n > > > qemu process. > >=20 > > That's no problem - virtio-gpu crashes, it disappears from the dbus > > bus, but everything else keeps running. >=20 > Crashing is the easy case; assume it's malicious and you don't want it > getting to say a storage device provided by another vhost-user device. If we assume that the 2 processes can't commnuicate / access each other outside DBus, then the attack avenues added by use of dbus are most likely either: - invoking some DBus method that should not be allowed due to incomplete dbus security policy.=20 - finding a crash in a dbus client library that you can somehow exploit to get remote code execution in the separate process I won't claim this is impossible, but I think it helps to be using a standard, widely used battle tested RPC impl, rather than a home grown RPC protocol. > > > > But if necessary, dbus can enforce policies on who is allowed to = own a > > > > name, or to send/receive message from. As far as I know, this is > > > > mostly user/group policies. > > > >=20 > > > > But there is also SELinux checks to send_msg and acquire_svc (see > > > > dbus-daemon(1)) > > >=20 > > > But how does something like SELinux interact with a private dbus=20 > > > rather than the system dbus? > >=20 > > There's already two dbus-daemon's on each host - the system one and > > the session one, and they get different selinux contexts, > > system_dbus_t and unconfined_dbus_t. > >=20 > > Since libvirt would be responsible for launching these private dbus > > daemons it would be easy to make it run svirt_dbus_t for example. > > Actually it would be svirt_dbus_t:s0:cNNN,cMMM to get uniqueness > > per VM. > >=20 > > Will of course require us to talk to the SELinux maintainers to > > get some sensible policy rules created. >=20 > This all relies on SELinux and running privileged qemu/vhost-user pairs= ; > needing to do that purely to enforce security seems wrong. Compare to an alternative bus-less solution where each helper has a direct UNIX socket connection to QEMU. If two helpers are running as the same user ID, then can still directly attack each other via things like ptrace or /proc/$PID/mem, unless you've used SELinux to isolate them, or run each as a distinct user ID. If you do the latter, then we can still easily isolate them using dbus. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|