CVE-2024-35791

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

KVM: SVM: Flush pages under kvm->lock to fix UAF in svm_register_enc_region()

Do the cache flush of converted pages in svm_register_enc_region() before

dropping kvm->lock to fix use-after-free issues where region and/or its

array of pages could be freed by a different task, e.g. if userspace has

__unregister_enc_region_locked() already queued up for the region.

Note, the "obvious" alternative of using local variables doesn't fully

resolve the bug, as region->pages is also dynamically allocated. I.e. the

region structure itself would be fine, but region->pages could be freed.

Flushing multiple pages under kvm->lock is unfortunate, but the entire

flow is a rare slow path, and the manual flush is only needed on CPUs that

lack coherency for encrypted memory.