Re: [PATCH v4] iommu/s390: Implement blocking domain

[Jason Gunthorpe]

On Tue, Sep 10, 2024 at 05:15:16PM -0400, Matthew Rosato wrote:
> This fixes a crash when surprise hot-unplugging a PCI device. This crash
> happens because during hot-unplug __iommu_group_set_domain_nofail()
> attaching the default domain fails when the platform no longer
> recognizes the device as it has already been removed and we end up with
> a NULL domain pointer and UAF. This is exactly the case referred to in
> the second comment in __iommu_device_set_domain() and just as stated
> there if we can instead attach the blocking domain the UAF is prevented
> as this can handle the already removed device. Implement the blocking
> domain to use this handling.  With this change, the crash is fixed but
> we still hit a warning attempting to change DMA ownership on a blocked
> device.
> 
> Fixes: c76c067e488c ("s390/pci: Use dma-iommu layer")
> Co-developed-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> ---
> Changes for v4:
> - fix lockdep assert
> Changes for v3:
> - make blocking_domain type iommu_domain
> - change zdev->s390_domain to type iommu_domain and remove most uses
> - remove s390_iommu_detach_device, use blocking domain attach
> - add spinlock to serialize zdev->s390_domain change / access to counters
> ---
>  arch/s390/include/asm/pci.h |  4 +-
>  arch/s390/pci/pci.c         |  3 ++
>  arch/s390/pci/pci_debug.c   | 10 ++++-
>  drivers/iommu/s390-iommu.c  | 73 +++++++++++++++++++++++--------------
>  4 files changed, 59 insertions(+), 31 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason