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

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-05-22 · updated 2026-08-04

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().

Affected products

Linux kernel: from 5.13 before 5.14.15; 5.15-rc1, 5.15-rc2, 5.15-rc3, 5.15-rc4, 5.15-rc5, 5.15-rc6 — fixed in 5.14.15

How to fix

Upgrade to a fixed version: Linux kernel 5.14.15. Check the vendor advisory for mitigations.

References

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