[0/3] vfio-pci: Block user access to disabled device MMIO

Message

Alex Williamson May 1, 2020, 9:38 p.m. UTC

Add tracking of the device memory enable bit and block/fault accesses
to device MMIO space while disabled.  This provides synchronous fault
handling for CPU accesses to the device and prevents the user from
triggering platform level error handling present on some systems.
Device reset and MSI-X vector table accesses are also included such
that access is blocked across reset and vector table accesses do not
depend on the user configuration of the device.

This is based on the vfio for-linus branch currently in next, making
use of follow_pfn() in vaddr_get_pfn() and therefore requiring patch
1/ to force the user fault in the case that a PFNMAP vma might be
DMA mapped before user access.  Further PFNMAP iommu invalidation
tracking is not yet included here.

As noted in the comments, I'm copying quite a bit of the logic from
rdma code for performing the zap_vma_ptes() calls and I'm also
attempting to resolve lock ordering issues in the fault handler to
lockdep's satisfaction.  I appreciate extra eyes on these sections in
particular.

I expect this to be functionally equivalent for any well behaved
userspace driver, but obviously there is a potential for the user to
get -EIO or SIGBUS on device access.  The device is provided to the
user enabled and device resets will restore the command register, so
by my evaluation a user would need to explicitly disable the memory
enable bit to trigger these faults.  We could potentially remap vmas
to a zero page rather than SIGBUS if we experience regressions, but
without known code requiring that, SIGBUS seems the appropriate
response to this condition.  Thanks,

Alex

---

Alex Williamson (3):
      vfio/type1: Support faulting PFNMAP vmas
      vfio-pci: Fault mmaps to enable vma tracking
      vfio-pci: Invalidate mmaps and block MMIO access on disabled memory


 drivers/vfio/pci/vfio_pci.c         |  268 +++++++++++++++++++++++++++++++++--
 drivers/vfio/pci/vfio_pci_config.c  |   31 ++++
 drivers/vfio/pci/vfio_pci_intrs.c   |   18 ++
 drivers/vfio/pci/vfio_pci_private.h |   11 +
 drivers/vfio/pci/vfio_pci_rdwr.c    |   12 ++
 drivers/vfio/vfio_iommu_type1.c     |   36 ++++-
 6 files changed, 356 insertions(+), 20 deletions(-)