From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:50578)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1RFt4v-0001Uc-IN
	for qemu-devel@nongnu.org; Mon, 17 Oct 2011 15:42:30 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1RFt4u-0003sC-JG
	for qemu-devel@nongnu.org; Mon, 17 Oct 2011 15:42:29 -0400
Received: from mx1.redhat.com ([209.132.183.28]:13949)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1RFt4u-0003s8-9c
	for qemu-devel@nongnu.org; Mon, 17 Oct 2011 15:42:28 -0400
Date: Mon, 17 Oct 2011 21:43:31 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20111017194330.GA10756@redhat.com>
References: <cover.1318843693.git.jan.kiszka@siemens.com>
	<57386830befff359aa6eac1610816eb9c853a05d.1318843693.git.jan.kiszka@siemens.com>
	<20111017111045.GB4537@redhat.com> <4E9C1042.4040007@siemens.com>
	<20111017115721.GF4537@redhat.com> <4E9C1A6E.1010404@siemens.com>
	<20111017125031.GJ4537@redhat.com> <4E9C7DE1.3030706@web.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4E9C7DE1.3030706@web.de>
Subject: Re: [Qemu-devel] [RFC][PATCH 06/45] msix: Prevent bogus mask
 updates on MMIO accesses
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Jan Kiszka <jan.kiszka@web.de>
Cc: Alex Williamson <alex.williamson@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, Avi Kivity <avi@redhat.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

On Mon, Oct 17, 2011 at 09:11:29PM +0200, Jan Kiszka wrote:
> On 2011-10-17 14:50, Michael S. Tsirkin wrote:
> > On Mon, Oct 17, 2011 at 02:07:10PM +0200, Jan Kiszka wrote:
> >> On 2011-10-17 13:57, Michael S. Tsirkin wrote:
> >>> On Mon, Oct 17, 2011 at 01:23:46PM +0200, Jan Kiszka wrote:
> >>>> On 2011-10-17 13:10, Michael S. Tsirkin wrote:
> >>>>> On Mon, Oct 17, 2011 at 11:27:40AM +0200, Jan Kiszka wrote:
> >>>>>> Only accesses to the MSI-X table must trigger a call to
> >>>>>> msix_handle_mask_update or a notifier invocation.
> >>>>>>
> >>>>>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> >>>>>
> >>>>> Why would msix_mmio_write be called on an access
> >>>>> outside the table?
> >>>>
> >>>> Because it handles both the table and the PBA.
> >>>
> >>> Hmm. Interesting. Is there a bug in how we handle PBA
> >>> updates then? If yes I'd like a separate patch for that
> >>> to apply to the stable tree.
> >>
> >> I first thought it was a serious bug, but it just triggers if the guest
> >> write to PBA (which is very uncommon) and that actually triggers any
> >> spurious out-of-bounds vector injection. Highly unlikely.
> > 
> > Yes guests don't really use PBA ATM. But is there something
> > bad a malicious guest can do? For example, what if
> > msix_clr_pending gets invoked with this huge vector value?
> > 
> > It does seem serious ...
> 
> I checked it before and I think it is harmless. The largest vector that
> can be miscalculated is 255. But bit 255 in the PBA is still safe inside
> our MMIO page.
> 
> Jan
> 

you are right. we got lucky.