{"id":"CVE-2026-89961","state":"PUBLISHED","title":"powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population","description":"In the Linux kernel, the following vulnerability has been resolved:\n\npowerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population\n\nvmemmap_populate_compound_pages() uses addr_pfn to determine the PFN\noffset within a compound page and to decide whether the current vmemmap\nslot should be populated as a head page mapping or should reuse a tail\npage mapping.\n\nHowever, addr_pfn is advanced manually in parallel with addr.  The loop\nitself progresses in vmemmap address space, so each PAGE_SIZE step in addr\ncovers PAGE_SIZE / sizeof(struct page) struct page slots.  Since addr_pfn\nis compared against nr_pages in data-PFN units, it should advance by the\nsame number of PFNs.  The existing manual increments do not match that and\ntherefore do not reliably track the PFN corresponding to the current addr.\n\nAs a result, pfn_offset can be computed from the wrong PFN and the code\ncan make the head/tail decision for the wrong compound-page position.\n\nFix this by deriving addr_pfn directly from the current vmemmap address\ninstead of carrying it as loop state.","publishedAt":"2026-09-16T10:32:43.921Z","updatedAt":"2026-10-19T08:55:35.034Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"f2b79c0d79683d552369bb9a7282c1f0226fc566","status":"affected","lessThan":"b96be860673f9fbbf12cdadb0b25fc4d6d4d207f","versionType":"git"},{"version":"f2b79c0d79683d552369bb9a7282c1f0226fc566","status":"affected","lessThan":"e163c7184acf36ac20a248498f4a16016057ca01","versionType":"git"},{"version":"f2b79c0d79683d552369bb9a7282c1f0226fc566","status":"affected","lessThan":"9c914b7a0bd18834505c65f22225ce22c152b2d9","versionType":"git"},{"version":"f2b79c0d79683d552369bb9a7282c1f0226fc566","status":"affected","lessThan":"7968852a7ca3ce81477ec5b4494a28d612f35a97","versionType":"git"},{"version":"f2b79c0d79683d552369bb9a7282c1f0226fc566","status":"affected","lessThan":"89a4ae32764172468dea303eb6ae90fe6c859712","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/powerpc/mm/book3s64/radix_pgtable.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.6","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.6","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.110","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.51","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.5","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/powerpc/mm/book3s64/radix_pgtable.c"]}],"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"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:26.108Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89961.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89961","state":"PUBLISHED","datePublished":"2026-09-16T10:32:43.921Z","dateUpdated":"2026-10-19T08:55:35.034Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.778Z"},"containers":{"cna":{"title":"powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\npowerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population\n\nvmemmap_populate_compound_pages() uses addr_pfn to determine the PFN\noffset within a compound page and to decide whether the current vmemmap\nslot should be populated as a head page mapping or should reuse a tail\npage mapping.\n\nHowever, addr_pfn is advanced manually in parallel with addr.  The loop\nitself progresses in vmemmap address space, so each PAGE_SIZE step in addr\ncovers PAGE_SIZE / sizeof(struct page) struct page slots.  Since addr_pfn\nis compared against nr_pages in data-PFN units, it should advance by the\nsame number of PFNs.  The existing manual increments do not match that and\ntherefore do not reliably track the PFN corresponding to the current addr.\n\nAs a result, pfn_offset can be computed from the wrong PFN and the code\ncan make the head/tail decision for the wrong compound-page position.\n\nFix this by deriving addr_pfn directly from the current vmemmap address\ninstead of carrying it as loop state."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"f2b79c0d79683d552369bb9a7282c1f0226fc566","status":"affected","lessThan":"b96be860673f9fbbf12cdadb0b25fc4d6d4d207f","versionType":"git"},{"version":"f2b79c0d79683d552369bb9a7282c1f0226fc566","status":"affected","lessThan":"e163c7184acf36ac20a248498f4a16016057ca01","versionType":"git"},{"version":"f2b79c0d79683d552369bb9a7282c1f0226fc566","status":"affected","lessThan":"9c914b7a0bd18834505c65f22225ce22c152b2d9","versionType":"git"},{"version":"f2b79c0d79683d552369bb9a7282c1f0226fc566","status":"affected","lessThan":"7968852a7ca3ce81477ec5b4494a28d612f35a97","versionType":"git"},{"version":"f2b79c0d79683d552369bb9a7282c1f0226fc566","status":"affected","lessThan":"89a4ae32764172468dea303eb6ae90fe6c859712","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/powerpc/mm/book3s64/radix_pgtable.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.6","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.6","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.110","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.51","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.5","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/powerpc/mm/book3s64/radix_pgtable.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/b96be860673f9fbbf12cdadb0b25fc4d6d4d207f"},{"url":"https://git.kernel.org/stable/c/e163c7184acf36ac20a248498f4a16016057ca01"},{"url":"https://git.kernel.org/stable/c/9c914b7a0bd18834505c65f22225ce22c152b2d9"},{"url":"https://git.kernel.org/stable/c/7968852a7ca3ce81477ec5b4494a28d612f35a97"},{"url":"https://git.kernel.org/stable/c/89a4ae32764172468dea303eb6ae90fe6c859712"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The bug is in powerpc radix vmemmap_populate_compound_pages(), reached only through local ZONE_DEVICE hotplug (dev_dax_probe → devm_memremap_pages → arch_add_memory → sparse_add_section). It is not reachable from network protocols, Bluetooth, or USB.\nAC:L - Once device-DAX with compound vmemmap is mapped (2MB PMD on 4K kernels or 1GB PUD on 64K, the documented powerpc DAX configs), addr_pfn drifts on every loop iteration and the wrong head/tail mapping is deterministic; no race or attacker-uncontrollable layout is required.\nPR:L - Initial memremap requires administrator DAX setup, but on a provisioned persistent-memory or cloud POWER server an unprivileged local user with /dev/dax access can mmap the device and drive kernel use of the mis-aliased struct pages via faults and GUP without init-namespace CAP_SYS_ADMIN.\nUI:N - Exploitation needs no victim action; the attacker mmaps or faults the already-provisioned DAX device themselves. No mount, click, or hotplug by another user is required at exploit time.\nS:U - Impact is kernel struct-page aliasing and MM corruption inside the same host kernel security authority. It is not a KVM guest-to-host escape, IOMMU/DMA bypass, or sandbox boundary crossing.\nC:H - Wrong pfn_offset aliases distinct vmemmap pages so different DAX PFNs share struct-page backing; later memmap_init, faults, and GUP read corrupted flags, mapping, and compound-head fields, disclosing kernel memory via that metadata.\nI:H - The same aliases turn kernel writes (page init, folio mapping, refcount, compound head/tail linkage) into writes to the wrong struct pages, an exploitable kernel memory-corruption primitive that can hijack control flow rather than a bounded data modification.\nA:H - Mis-linked compound pages and aliased vmemmap cause kernel oops, BUG_ON, or panic when MM code walks folio heads, refcounts, or DAX fault handlers, fully denying availability of the affected POWER radix host."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:55:35.034Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6","versionEndExcluding":"6.6.157"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6","versionEndExcluding":"6.12.110"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6","versionEndExcluding":"6.18.51"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6","versionEndExcluding":"7.2.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}