Subject: CVE-2021-46977: KVM: VMX: Disable preemption when probing user return MSRs

From: Greg Kroah-Hartman <[email-masked]>

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

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

KVM: VMX: Disable preemption when probing user return MSRs

Disable preemption when probing a user return MSR via RDSMR/WRMSR.  If
the MSR holds a different value per logical CPU, the WRMSR could corrupt
the host's value if KVM is preempted between the RDMSR and WRMSR, and
then rescheduled on a different CPU.

Opportunistically land the helper in common x86, SVM will use the helper
in a future commit.

The Linux kernel CVE team has assigned CVE-2021-46977 to this issue.

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

	Issue introduced in 5.5 with commit 4be534102624 and fixed in 5.10.38 with commit 31f29749ee97
	Issue introduced in 5.5 with commit 4be534102624 and fixed in 5.11.22 with commit 5adcdeb57007
	Issue introduced in 5.5 with commit 4be534102624 and fixed in 5.12.5 with commit e3ea1895df71
	Issue introduced in 5.5 with commit 4be534102624 and fixed in 5.13 with commit 5104d7ffcf24

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-2021-46977
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_host.h
	arch/x86/kvm/vmx/vmx.c
	arch/x86/kvm/x86.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/31f29749ee970c251b3a7e5b914108425940d089
	https://git.kernel.org/stable/c/5adcdeb57007ccf8ab7ac20bf787ffb6fafb1a94
	https://git.kernel.org/stable/c/e3ea1895df719c4ef87862501bb10d95f4177bed
	https://git.kernel.org/stable/c/5104d7ffcf24749939bea7fdb5378d186473f890