Re: [Xen-devel] [PATCH v3 4/6] xen/x86: Allow stubdom access to irq created for msi.

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Mon, Jan 28, 2019 at 02:50:00PM +0000, Wei Liu wrote:
> On Sat, Jan 26, 2019 at 03:31:15AM +0100, Marek Marczykowski-Górecki wrote:
> > From: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>
> > 
> > Stubdomains need to be given sufficient privilege over the guest which it
> > provides emulation for in order for PCI passthrough to work correctly.
> > When a HVM domain try to enable MSI, QEMU in stubdomain calls
> > PHYSDEVOP_map_pirq, but later it needs to call XEN_DOMCTL_bind_pt_irq as
> > part of xc_domain_update_msi_irq. Allow for that as part of
> > PHYSDEVOP_map_pirq.
> > 
> > This is not needed for PCI INTx, because IRQ in that case is known
> > beforehand and the stubdomain is given permissions over this IRQ by
> > libxl__device_pci_add (there's a do_pci_add against the stubdomain).
> > 
> > Based on 
> > https://github.com/OpenXT/xenclient-oe/blob/5e0e7304a5a3c75ef01240a1e3673665b2aaf05e/recipes-extended/xen/files/stubdomain-msi-irq-access.patch
> >  by Eric Chanudet <chanudete@xxxxxxxxxxxx>.
> > 
> > Signed-off-by: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> > ---
> > Changes in v3:
> >  - extend commit message
> > 
> > With this patch, stubdomain will be able to create and map multiple irq
> > (DoS possibility?), as only target domain is validated in practice. Is
> > that ok? If not, what additional limits could be applied here?
> > In INTx case the problem doesn't apply, because toolstack grant access
> > to particular IRQ and no allocation happen on stubdomain request. But in
> > MSI case, it isn't that easy as IRQ number isn't known before (as
> > explained in the commit message).
> > ---
> >  xen/arch/x86/irq.c     | 23 +++++++++++++++++++++++
> >  xen/arch/x86/physdev.c |  9 +++++++++
> >  2 files changed, 32 insertions(+)
> > 
> > diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
> > index 8b44d6c..67c67d4 100644
> > --- a/xen/arch/x86/irq.c
> > +++ b/xen/arch/x86/irq.c
> > @@ -2674,6 +2674,21 @@ int allocate_and_map_msi_pirq(struct domain *d, int 
> > index, int *pirq_p,
> >          {
> >      case MAP_PIRQ_TYPE_MULTI_MSI:
> >              irq = create_irq(NUMA_NO_NODE);
> > +            if ( !(irq < nr_irqs_gsi || irq >= nr_irqs) &&
> > +                    current->domain->target == d )
> > +            {
> > +                ret = irq_permit_access(current->domain, irq);
> > +                if ( ret ) {
> > +                    dprintk(XENLOG_G_ERR,
> > +                            "dom%d: can't grant it's stubdom (%d) access 
> > to "
> > +                            "irq %d for msi: %d!\n",
> > +                            d->domain_id,
> > +                            current->domain->domain_id,
> > +                            irq,
> > +                            ret);
> > +                    return ret;
> 
> Don't you need to deallocate the irq before returning?

Yes, indeed.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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