Subject: CVE-2021-47450: KVM: arm64: Fix host stage-2 PGD refcount

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

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

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

KVM: arm64: Fix host stage-2 PGD refcount

The KVM page-table library refcounts the pages of concatenated stage-2
PGDs individually. However, when running KVM in protected mode, the
host's stage-2 PGD is currently managed by EL2 as a single high-order
compound page, which can cause the refcount of the tail pages to reach 0
when they shouldn't, hence corrupting the page-table.

Fix this by introducing a new hyp_split_page() helper in the EL2 page
allocator (matching the kernel's split_page() function), and make use of
it from host_s2_zalloc_pages_exact().

The Linux kernel CVE team has assigned CVE-2021-47450 to this issue.

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

	Issue introduced in 5.13 with commit 1025c8c0c6ac and fixed in 5.14.15 with commit b372264c66ef
	Issue introduced in 5.13 with commit 1025c8c0c6ac and fixed in 5.15 with commit 1d58a17ef545

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-2021-47450
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/arm64/kvm/hyp/include/nvhe/gfp.h
	arch/arm64/kvm/hyp/nvhe/mem_protect.c
	arch/arm64/kvm/hyp/nvhe/page_alloc.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/b372264c66ef78f2cab44e877fbd765ad6d24c39
	https://git.kernel.org/stable/c/1d58a17ef54599506d44c45ac95be27273a4d2b1