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

Vulnerability Description

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.

References

• https://git.kernel.org/stable/c/2d13b79640b147bd77c34a5998533b2021a4122d
• https://git.kernel.org/stable/c/e126b508ed2e616d679d85fca2fbe77bb48bbdd7
• https://git.kernel.org/stable/c/4868c0ecdb6cfde7c70cf478c46e06bb9c7e5865
• https://git.kernel.org/stable/c/12f8e32a5a389a5d58afc67728c76e61beee1ad4
• https://git.kernel.org/stable/c/f6d53d8a2617dd58c89171a6b9610c470ebda38a
• https://git.kernel.org/stable/c/5ef1d8c1ddbf696e47b226e11888eaf8d9e8e807