Bug 2347787 (CVE-2022-49562)

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

KVM: x86: Use __try_cmpxchg_user() to update guest PTE A/D bits

Use the recently introduced __try_cmpxchg_user() to update guest PTE A/D
bits instead of mapping the PTE into kernel address space.  The VM_PFNMAP
path is broken as it assumes that vm_pgoff is the base pfn of the mapped
VMA range, which is conceptually wrong as vm_pgoff is the offset relative
to the file and has nothing to do with the pfn.  The horrific hack worked
for the original use case (backing guest memory with /dev/mem), but leads
to accessing "random" pfns for pretty much any other VM_PFNMAP case.