Subject: CVE-2021-47389: KVM: SVM: fix missing sev_decommission in sev_receive_start

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

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

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

KVM: SVM: fix missing sev_decommission in sev_receive_start

DECOMMISSION the current SEV context if binding an ASID fails after
RECEIVE_START.  Per AMD's SEV API, RECEIVE_START generates a new guest
context and thus needs to be paired with DECOMMISSION:

     The RECEIVE_START command is the only command other than the LAUNCH_START
     command that generates a new guest context and guest handle.

The missing DECOMMISSION can result in subsequent SEV launch failures,
as the firmware leaks memory and might not able to allocate more SEV
guest contexts in the future.

Note, LAUNCH_START suffered the same bug, but was previously fixed by
commit 934002cd660b ("KVM: SVM: Call SEV Guest Decommission if ASID
binding fails").

The Linux kernel CVE team has assigned CVE-2021-47389 to this issue.

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

	Issue introduced in 5.13 with commit af43cbbf954b and fixed in 5.14.10 with commit efd7866e114d
	Issue introduced in 5.13 with commit af43cbbf954b and fixed in 5.15 with commit f1815e0aa770

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-2021-47389
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/efd7866e114dcb44f86d151e843f8276b7efbc67
	https://git.kernel.org/stable/c/f1815e0aa770f2127c5df31eb5c2f0e37b60fa77