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

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Friday, September 11, 2015 4:56 PM
> 
> >>> On 11.09.15 at 01:22, <kevin.tian@xxxxxxxxx> wrote:
> > Sorry it's a bad example. My actual concern is that we can't count
> > on this per-VM relax/strict policy to prevent group devices assigned
> > to different VM. In that case it's definitely a security hole since
> > one VM may clobber shared RMRR to impact another VM. So right
> > example for that scenario is both VMs specified with 'relax'.
> 
> Sorry, no, the idea of "relax" is to allow the admin to state "I have
> no security concerns". Hence we'd have a security issue only if the
> default was "relax" (which iiuc it isn't, or if it were _that's_ what
> would need to be alongside the presented change). Whether that
> statement of the admin is because of
> - knowing that the RMRR won't be used post-boot
> - group-assigning the devices manually
> - simply not caring (i.e. trusting the guests)
> is not our business.
> 
> IOW, provided there's no way for "relax" to become the default
> (Tiejun - please confirm), the patch as is should be fine.
> 
> Jan
> 

OK, that explanation is fine to me as long as it's made clear no
security guarantee once admin uses 'relax' for any domain. Tiejun
could you resend patch with right warning/error type?

Thanks
Kevin

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