RE: [PATCH 0/9 v2] vfio-pci: add support for Freescale IOMMU (PAMU)

[Bharat.Bhushan@xxxxxxxxxxxxx]

> -----Original Message-----
> From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
> Sent: Saturday, December 07, 2013 1:00 AM
> To: Wood Scott-B07421
> Cc: Bhushan Bharat-R65777; linux-pci@xxxxxxxxxxxxxxx; agraf@xxxxxxx; Yoder
> Stuart-B08248; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; bhelgaas@xxxxxxxxxx; linuxppc-
> dev@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH 0/9 v2] vfio-pci: add support for Freescale IOMMU (PAMU)
> 
> On Fri, 2013-12-06 at 12:59 -0600, Scott Wood wrote:
> > On Thu, 2013-12-05 at 22:11 -0600, Bharat Bhushan wrote:
> > >
> > > > -----Original Message-----
> > > > From: Wood Scott-B07421
> > > > Sent: Friday, December 06, 2013 5:52 AM
> > > > To: Bhushan Bharat-R65777
> > > > Cc: Alex Williamson; linux-pci@xxxxxxxxxxxxxxx; agraf@xxxxxxx;
> > > > Yoder Stuart- B08248; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx;
> > > > bhelgaas@xxxxxxxxxx; linuxppc- dev@xxxxxxxxxxxxxxxx;
> > > > linux-kernel@xxxxxxxxxxxxxxx
> > > > Subject: Re: [PATCH 0/9 v2] vfio-pci: add support for Freescale
> > > > IOMMU (PAMU)
> > > >
> > > > On Thu, 2013-11-28 at 03:19 -0600, Bharat Bhushan wrote:
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Bhushan Bharat-R65777
> > > > > > Sent: Wednesday, November 27, 2013 9:39 PM
> > > > > > To: 'Alex Williamson'
> > > > > > Cc: Wood Scott-B07421; linux-pci@xxxxxxxxxxxxxxx;
> > > > > > agraf@xxxxxxx; Yoder Stuart- B08248;
> > > > > > iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; bhelgaas@xxxxxxxxxx;
> > > > > > linuxppc- dev@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > > > > > Subject: RE: [PATCH 0/9 v2] vfio-pci: add support for
> > > > > > Freescale IOMMU (PAMU)
> > > > > >
> > > > > > If we just provide the size of MSI bank to userspace then
> > > > > > userspace cannot do anything wrong.
> > > > >
> > > > > So userspace does not know address, so it cannot mmap and cause
> > > > > any
> > > > interference by directly reading/writing.
> > > >
> > > > That's security through obscurity...  Couldn't the malicious user
> > > > find out the address via other means, such as experimentation on
> > > > another system over which they have full control?  What would
> > > > happen if the user reads from their device's PCI config space?  Or
> > > > gets the information via some back door in the PCI device they
> > > > own?  Or pokes throughout the address space looking for something that
> generates an interrupt to its own device?
> > >
> > > So how to solve this problem, Any suggestion ?
> > >
> > > We have to map one window in PAMU for MSIs and a malicious user can
> > > ask its device to do DMA to MSI window region with any pair of
> > > address and data, which can lead to unexpected MSIs in system?
> >
> > I don't think there are any solutions other than to limit each bank to
> > one user, unless the admin turns some knob that says they're OK with
> > the partial loss of isolation.
> 
> Even if the admin does opt-in to an allow_unsafe_interrupts options, it should
> still be reasonably difficult for one guest to interfere with the other.  I
> don't think we want to rely on the blind luck of making the full MSI bank
> accessible to multiple guests and hoping they don't step on each other.

Not sure how to solve in this case (sharing MSI page)

>  That probably means that vfio needs to manage the space rather than the guest.

What you mean by " vfio needs to manage the space rather than the guest"?

Thanks
-Bharat

> Thanks,
> 
> Alex
> 

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