CVE-2026-89961
HighCVSS 7.8Summary
In the Linux kernel, vmemmap_populate_compound_pages() on powerpc manually advanced addr_pfn in a way that did not match the loop's progression through vmemmap addresses. This caused pfn_offset to be computed from the wrong PFN and led to incorrect head/tail mapping decisions for compound pages.
Risk Assessment
Incorrect PFN tracking in vmemmap population can lead to memory corruption or kernel misbehavior on powerpc systems using compound pages.
Recommendation
Update the Linux kernel to a version containing the fix that derives addr_pfn directly from the current vmemmap address instead of carrying it as loop state.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS