linux-cve-announce - CVE-2022-49562: KVM: x86: Use __try_cmpxchg

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Message-ID: <2025022618-CVE-2022-49562-1d2c@gregkh>
Date: Wed, 26 Feb 2025 03:13:56 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2022-49562: KVM: x86: Use __try_cmpxchg_user() to update guest PTE A/D bits

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2022-49562 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.2 with commit bd53cb35a3e9adb73a834a36586e9ad80e877767 and fixed in 5.17.13 with commit 38b888911e8dc89b89d8147cfb1d2dbe6373bf78
	Issue introduced in 5.2 with commit bd53cb35a3e9adb73a834a36586e9ad80e877767 and fixed in 5.18.2 with commit 8089e5e1d18402fb8152d6b6815450a36fffa9b0
	Issue introduced in 5.2 with commit bd53cb35a3e9adb73a834a36586e9ad80e877767 and fixed in 5.19 with commit f122dfe4476890d60b8c679128cd2259ec96a24c

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2022-49562
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	arch/x86/kvm/mmu/paging_tmpl.h


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/38b888911e8dc89b89d8147cfb1d2dbe6373bf78
	https://git.kernel.org/stable/c/8089e5e1d18402fb8152d6b6815450a36fffa9b0
	https://git.kernel.org/stable/c/f122dfe4476890d60b8c679128cd2259ec96a24c