GHSA-wwj6-vghv-5p64: Kata Container to Guest micro VM privilege escalation

Summary An issue in Kata with Cloud Hypervisor allows a user of the container to modify the file system used by the Guest micro VM ultimately achieving arbitrary code execution as root in said VM. The current understinding is this doesn’t impact the security of the Host or of other containers / VMs running on that Host (note that arm64 QEMU lacks NVDIMM read-only support: It is believed that until the upstream QEMU gains this capability, a guest write could reach the image file). Details _Linux virtio-pmem_ The virtio-pmem probe path always registers the region as a generic pagemap that supports asynchronous flushes, but it never marks the region as read-only. Only the ND_REGION_PAGEMAP and ND_REGION_ASYNC bits are set before the region is created, so nd_region->ro always stays cleared and the block device is left writable. Later, pmem_attach_disk() wires the region into the block layer with full read/write semantics – the block device operations call pmem_do_write() which performs cache-flushed memcpy operations directly into the host-provided shared memory window. nvdimm_check_and_set_ro() would set the disk read-only if the region had been flagged as such, but because virtio_pmem never sets that flag, the helper becomes a no-op. _Cloud-Hypervisor virtio_pmem_ discard_writes=on causes the file backing the virtio-pmem device to be opened read-only and mapped with MAP_PRIVATE rather than MAP_SHARED. That combination means the guest can modify the private copy of the mapped pages, but those modifications never propagate back to the underlying file. The guest (and Cloud Hypervisor process) will still read the modified data because it lives in the private copy of the mapping, so write-then-read sequences appear to succeed even though nothing is persisted. Once the mapping is dropped or the VM is restarted, those copy-on-write changes disappear, leaving the backing file unchanged. _Kata /dev/pmem0_ Kata boots each pod/VM by DAX-mapping a read-only guest image from