In the Linux kernel, the following vulnerability has been resolved:

iommu/amd: Clear DMA ops when switching domain

Since commit 08a27c1c3ecf (iommu: Add support to change default domain of an iommu group) a user can switch a device between IOMMU and direct DMA through sysfs. This doesnt work for AMD IOMMU at the moment because dev->dma_ops is not cleared when switching from a DMA to an identity IOMMU domain. The DMA layer thus attempts to use the dma-iommu ops on an identity domain, causing an oops:

echo 0000:00:05.0 > /sys/sys/bus/pci/drivers/e1000e/unbind

echo identity > /sys/bus/pci/devices/0000:00:05.0/iommu_group/type

echo 0000:00:05.0 > /sys/sys/bus/pci/drivers/e1000e/bind

… BUG: kernel NULL pointer dereference, address: 0000000000000028 … Call Trace: iommu_dma_alloc e1000e_setup_tx_resources e1000e_open

Since iommu_change_dev_def_domain() calls probe_finalize() again, clear the dma_ops there like Vt-d does.

References

• https://git.kernel.org/stable/c/d6177a6556f853785867e2ec6d5b7f4906f0d809
• https://git.kernel.org/stable/c/f3f2cf46291a693eab21adb94171b0128c2a9ec1