Re: [Xen-devel] [PATCH 0/11] Xen PCI Passthrough security fixes

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 17 Jun 2015, Ian Campbell wrote:
> On Tue, 2015-06-02 at 16:47 +0100, Ian Campbell wrote:
> 
> ping?

The QEMU patch series is already upstream in QEMU and qemu-xen, so I
think we can apply this patch to libxl now.


> > On Tue, 2015-06-02 at 16:08 +0100, Stefano Stabellini wrote:
> > > the following is a collection of QEMU security fixes for PCI Passthrough
> > > on Xen.
> > 
> > Part of this locks down the PCI cfg space emulation, which means we now
> > need a way for people to request the old "permissive" behaviour for
> > devices which need it. Per the xl docs:
> >         It is recommended to enable this option only for trusted VMs
> >         under administrator control.
> > 
> > The toolstack (libxl, xl etc) already support a permissive flag in the
> > domain cfg, and this series adds a new device property. All we need to
> > do is tie them together.
> > 
> > The simple version is below. I also have an incremental update which
> > uses the QMP device-list-properties command to probe for the presence of
> > this property (so things can automatically work with unpatches qemu). I
> > think it's not really necessary in this case.
> > 
> > Ian.
> > 
> > -----8>---------
> > 
> > From c395657b03a1e2b7616d987e7078694874981979 Mon Sep 17 00:00:00 2001
> > From: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > Date: Mon, 1 Jun 2015 11:32:23 +0100
> > Subject: [PATCH] tools: libxl: allow permissive qemu-upstream pci
> >  passthrough.
> > 
> > EMBARGOED UNTIL 2015-06-02 12:00 (WITH XSA-131 ET AL)
> > 
> > Since XSA-131 qemu-xen now restricts access to PCI cfg by default. In
> > order to allow local configuration of the existing libxl_device_pci
> > "permissive" flag needs to be plumbed through via the new QMP property
> > added by the XSA-131 patches.
> > 
> > Versions of QEMU prior to XSA-131 did not support this permissive
> > property, so we only pass it if it is true. Older versions only
> > supported permissive mode.
> > 
> > qemu-xen-traditional already supports the permissive mode setting via
> > xenstore.
> > 
> > Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>
> > ---
> > v2: Only set argument if permissive==true.
> > ---
> >  tools/libxl/libxl_qmp.c |   12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/tools/libxl/libxl_qmp.c b/tools/libxl/libxl_qmp.c
> > index 9aa7e2e..6484f5e 100644
> > --- a/tools/libxl/libxl_qmp.c
> > +++ b/tools/libxl/libxl_qmp.c
> > @@ -849,6 +849,18 @@ int libxl__qmp_pci_add(libxl__gc *gc, int domid, 
> > libxl_device_pci *pcidev)
> >          QMP_PARAMETERS_SPRINTF(&args, "addr", "%x.%x",
> >                                 PCI_SLOT(pcidev->vdevfn), 
> > PCI_FUNC(pcidev->vdevfn));
> >      }
> > +    /*
> > +     * Version of QEMU prior to the XSA-131 fix did not support this
> > +     * property and were effectively always in permissive mode. The
> > +     * fix for XSA-131 switched the default to be restricted by
> > +     * default and added the permissive property.
> > +     *
> > +     * Therefore in order to support both old and new QEMU we only set
> > +     * the permissive flag if it is true. Users of older QEMU have no
> > +     * reason to set the flag so this is ok.
> > +     */
> > +    if (pcidev->permissive)
> > +        qmp_parameters_add_bool(gc, &args, "permissive", true);
> >  
> >      rc = qmp_synchronous_send(qmp, "device_add", args,
> >                                NULL, NULL, qmp->timeout);
> 
> 

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