linux-cve-announce - CVE-2021-47110: x86/kvm: Disable kvmclock on all CPUs on shutdown

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Date: Fri, 15 Mar 2024 21:15:00 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2021-47110: x86/kvm: Disable kvmclock on all CPUs on shutdown

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

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

x86/kvm: Disable kvmclock on all CPUs on shutdown

Currenly, we disable kvmclock from machine_shutdown() hook and this
only happens for boot CPU. We need to disable it for all CPUs to
guard against memory corruption e.g. on restore from hibernate.

Note, writing '0' to kvmclock MSR doesn't clear memory location, it
just prevents hypervisor from updating the location so for the short
while after write and while CPU is still alive, the clock remains usable
and correct so we don't need to switch to some other clocksource.

The Linux kernel CVE team has assigned CVE-2021-47110 to this issue.


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

	Fixed in 5.4.125 with commit 9084fe1b3572
	Fixed in 5.10.43 with commit 3b0becf8b1ec
	Fixed in 5.12.10 with commit 1df2dc09926f
	Fixed in 5.13 with commit c02027b5742b

Please see https://www.kernel.org or 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-2021-47110
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/include/asm/kvm_para.h
	arch/x86/kernel/kvm.c
	arch/x86/kernel/kvmclock.c


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/9084fe1b3572664ad276f427dce575f580c9799a
	https://git.kernel.org/stable/c/3b0becf8b1ecf642a9edaf4c9628ffc641e490d6
	https://git.kernel.org/stable/c/1df2dc09926f61319116c80ee85701df33577d70
	https://git.kernel.org/stable/c/c02027b5742b5aa804ef08a4a9db433295533046