CVE-2021-47450

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().