Re: [Xen-devel] [v2][PATCH] xen/vtd/iommu: permit group devices to passthrough in relaxed mode

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.09.15 at 07:23, <kevin.tian@xxxxxxxxx> wrote:
>>  From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Wednesday, September 09, 2015 2:55 PM
>> 
>> >>> On 09.09.15 at 03:59, <tiejun.chen@xxxxxxxxx> wrote:
>> > @@ -2310,12 +2312,16 @@ static int intel_iommu_assign_device(
>> >               PCI_DEVFN2(bdf) == devfn &&
>> >               rmrr->scope.devices_cnt > 1 )
>> >          {
>> > -            printk(XENLOG_G_ERR VTDPREFIX
>> > -                   " cannot assign %04x:%02x:%02x.%u"
>> > +            bool_t relaxed = !!(flag & XEN_DOMCTL_DEV_RDM_RELAXED);
>> > +
>> > +            printk(XENLOG_G_WARNING VTDPREFIX
>> 
>> Well, I can live with this always being a warning, but it's not what I
>> had asked for. The VT-d maintainers will have to judge.
>> 
> 
> Need to have separate warning/error level for relax/strict.
> 
> However I don't think this patch is a right fix. So far relax/strict policy
> is per-domain. what about one VM specifies relax while another VM
> specifies strict when each is assigned with a device sharing rmrr
> with the other? In that case it becomes a system-wide security hole.

The one specifying "strict" won't gets its device assigned (due to
the code above, taking the path that was there already without
the patch), so I don't see the security issue.

Jan


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