linux-cve-announce - CVE-2021-47062: KVM: SVM: Use online_vcpus, not created

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Date: Thu, 29 Feb 2024 23:37:59 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2021-47062: KVM: SVM: Use online_vcpus, not created_vcpus, to iterate over vCPUs

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

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

KVM: SVM: Use online_vcpus, not created_vcpus, to iterate over vCPUs

Use the kvm_for_each_vcpu() helper to iterate over vCPUs when encrypting
VMSAs for SEV, which effectively switches to use online_vcpus instead of
created_vcpus.  This fixes a possible null-pointer dereference as
created_vcpus does not guarantee a vCPU exists, since it is updated at
the very beginning of KVM_CREATE_VCPU.  created_vcpus exists to allow the
bulk of vCPU creation to run in parallel, while still correctly
restricting the max number of max vCPUs.

The Linux kernel CVE team has assigned CVE-2021-47062 to this issue.


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

	Issue introduced in 5.11 with commit ad73109ae7ec and fixed in 5.11.21 with commit bd0cced2ae93
	Issue introduced in 5.11 with commit ad73109ae7ec and fixed in 5.12.4 with commit ba7bf5d6336a
	Issue introduced in 5.11 with commit ad73109ae7ec and fixed in 5.13 with commit c36b16d29f3a

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-2021-47062
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/svm/sev.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/bd0cced2ae93195668f983d443f7f17e8efd24d2
	https://git.kernel.org/stable/c/ba7bf5d6336aa9c0d977b161bfa420c56d46ee40
	https://git.kernel.org/stable/c/c36b16d29f3af5f32fc1b2a3401bf48f71cabee1