arch/x86/kvm/mmu/paging_tmpl.h in the Linux kernel before 5.12.11 incorrectly computes the access permissions of a shadow page, leading to a missing guest protection page fault.
https://lists.debian.org/debian-lts-announce/2021/12/msg00012.html
https://lists.debian.org/debian-lts-announce/2021/10/msg00010.html
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.12.11