# CVE-2021-47450: linux: In the Linux kernel, the following vulnerability has been resolved:  KVM: arm64: Fix host stage-2 PGD refcount  The K...

CVE-2021-47450 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-47450, released May 22, 2024. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-47450
- Priority: Routine
- CVSS: 5.5 (medium)
- EPSS: 0.0021
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 22, 2024

## 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().

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.15.3-1 | [DEBIAN-CVE-2021-47450](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47450.md) | May 22, 2024 |
| Linux | linux Debian 13.5 (trixie) | 5.15.3-1 | [DEBIAN-CVE-2021-47450](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47450.md) | May 22, 2024 |
| Linux | linux Debian 14 | 5.15.3-1 | [DEBIAN-CVE-2021-47450](https://patchblox.com/security/data/fix/linux/debian-cve-2021-47450.md) | May 22, 2024 |

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