KVM Archive on lore.kernel.org
 help / color / Atom feed
From: Peter Xu <peterx@redhat.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	cohuck@redhat.com, jgg@ziepe.ca
Subject: Re: [PATCH v2 0/3] vfio-pci: Block user access to disabled device MMIO
Date: Thu, 7 May 2020 22:31:56 -0400
Message-ID: <20200508023156.GV228260@xz-x1> (raw)
In-Reply-To: <20200507163437.77b4bf2e@x1.home>

On Thu, May 07, 2020 at 04:34:37PM -0600, Alex Williamson wrote:
> On Thu, 7 May 2020 17:59:08 -0400
> Peter Xu <peterx@redhat.com> wrote:
> 
> > On Tue, May 05, 2020 at 03:54:36PM -0600, Alex Williamson wrote:
> > > v2:
> > > 
> > > Locking in 3/ is substantially changed to avoid the retry scenario
> > > within the fault handler, therefore a caller who does not allow retry
> > > will no longer receive a SIGBUS on contention.  IOMMU invalidations
> > > are still not included here, I expect that will be a future follow-on
> > > change as we're not fundamentally changing that issue in this series.
> > > The 'add to vma list only on fault' behavior is also still included
> > > here, per the discussion I think it's still a valid approach and has
> > > some advantages, particularly in a VM scenario where we potentially
> > > defer the mapping until the MMIO BAR is actually DMA mapped into the
> > > VM address space (or the guest driver actually accesses the device
> > > if that DMA mapping is eliminated at some point).  Further discussion
> > > and review appreciated.  Thanks,  
> > 
> > Hi, Alex,
> > 
> > I have a general question on the series.
> > 
> > IIUC this series tries to protect illegal vfio userspace writes to device MMIO
> > regions which may cause platform-level issues.  That makes perfect sense to me.
> > However what if the write comes from the devices' side?  E.g.:
> > 
> >   - Device A maps MMIO region X
> > 
> >   - Device B do VFIO_IOMMU_DMA_MAP on Device A's MMIO region X
> >     (so X's MMIO PFNs are mapped in device B's IOMMU page table)
> > 
> >   - Device A clears PCI_COMMAND_MEMORY (reset, etc.)
> >     - this should zap all existing vmas that mapping region X, however device
> >       B's IOMMU page table is not aware of this?
> > 
> >   - Device B writes to MMIO region X of device A even if PCI_COMMAND_MEMORY
> >     cleared on device A's PCI_COMMAND register
> > 
> > Could this happen?
> 
> Yes, this can happen and Jason has brought up variations on this
> scenario that are important to fix as well.  I've got some ideas, but
> the access in this series was the current priority.  There are also
> issues in the above scenario that if a platform considers a DMA write
> to an invalid IOMMU PTE and triggering an IOMMU fault to have the same
> severity as the write to disabled MMIO space we've prevented, then our
> hands are tied.  Thanks,

I see the point now; it makes sense to start with a series like this. Thanks, Alex.

-- 
Peter Xu


      reply index

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-05 21:54 Alex Williamson
2020-05-05 21:54 ` [PATCH v2 1/3] vfio/type1: Support faulting PFNMAP vmas Alex Williamson
2020-05-07 21:24   ` Peter Xu
2020-05-07 21:47     ` Alex Williamson
2020-05-07 23:54     ` Jason Gunthorpe
2020-05-08  2:19       ` Peter Xu
2020-05-08 12:10         ` Jason Gunthorpe
2020-05-08 14:30           ` Peter Xu
2020-05-08 15:05             ` Jason Gunthorpe
2020-05-08 15:42               ` Alex Williamson
2020-05-08 16:05                 ` Peter Xu
2020-05-08 18:39   ` Peter Xu
2020-05-05 21:54 ` [PATCH v2 2/3] vfio-pci: Fault mmaps to enable vma tracking Alex Williamson
2020-05-07 21:47   ` Peter Xu
2020-05-07 22:03     ` Alex Williamson
2020-05-07 22:22       ` Peter Xu
2020-05-07 23:56         ` Jason Gunthorpe
2020-05-08  2:16           ` Peter Xu
2020-05-08  6:44             ` Jason Wang
2020-05-08 14:27               ` Peter Xu
2020-05-08 12:08             ` Jason Gunthorpe
2020-05-08 14:26               ` Peter Xu
2020-05-05 21:55 ` [PATCH v2 3/3] vfio-pci: Invalidate mmaps and block MMIO access on disabled memory Alex Williamson
2020-05-22  2:39   ` Qian Cai
2020-05-22  4:18     ` Alex Williamson
2020-05-07 21:59 ` [PATCH v2 0/3] vfio-pci: Block user access to disabled device MMIO Peter Xu
2020-05-07 22:34   ` Alex Williamson
2020-05-08  2:31     ` Peter Xu [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200508023156.GV228260@xz-x1 \
    --to=peterx@redhat.com \
    --cc=alex.williamson@redhat.com \
    --cc=cohuck@redhat.com \
    --cc=jgg@ziepe.ca \
    --cc=kvm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

KVM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvm/0 kvm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvm kvm/ https://lore.kernel.org/kvm \
		kvm@vger.kernel.org
	public-inbox-index kvm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.kvm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git