CVE-2022-49562 — KVM: x86: Use __try_cmpxchg_user() to update guest PTE A/D bits

Affected: Linux

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.

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CVE-2022-49562 — KVM: x86: Use __try_cmpxchg_user() to update guest PTE A/D bits