mm: move page table sync declarations to linux/pgtable.h

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2025-39844
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-09-19 16:15:43 UTC
Updated2026-05-12 13:17:15 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: mm: move page table sync declarations to linux/pgtable.h During our internal testing, we started observing intermittent boot failures when the machine uses 4-level paging and has a large amount of persistent memory: BUG: unable to handle page fault for address: ffffe70000000034 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI RIP: 0010:__init_single_page+0x9/0x6d Call Trace: <TASK> __init_zone_device_page+0x17/0x5d memmap_init_zone_device+0x154/0x1bb pagemap_range+0x2e0/0x40f memremap_pages+0x10b/0x2f0 devm_memremap_pages+0x1e/0x60 dev_dax_probe+0xce/0x2ec [device_dax] dax_bus_probe+0x6d/0xc9 [... snip ...] </TASK> It turns out that the kernel panics while initializing vmemmap (struct page array) when the vmemmap region spans two PGD entries, because the new PGD entry is only installed in init_mm.pgd, but not in the page tables of other tasks. And looking at __populate_section_memmap(): if (vmemmap_can_optimize(altmap, pgmap)) // does not sync top level page tables r = vmemmap_populate_compound_pages(pfn, start, end, nid, pgmap); else // sync top level page tables in x86 r = vmemmap_populate(start, end, nid, altmap); In the normal path, vmemmap_populate() in arch/x86/mm/init_64.c synchronizes the top level page table (See commit 9b861528a801 ("x86-64, mem: Update all PGDs for direct mapping and vmemmap mapping changes")) so that all tasks in the system can see the new vmemmap area. However, when vmemmap_can_optimize() returns true, the optimized path skips synchronization of top-level page tables. This is because vmemmap_populate_compound_pages() is implemented in core MM code, which does not handle synchronization of the top-level page tables. Instead, the core MM has historically relied on each architecture to perform this synchronization manually. We're not the first party to encounter a crash caused by not-sync'd top level page tables: earlier this year, Gwan-gyeong Mun attempted to address the issue [1] [2] after hitting a kernel panic when x86 code accessed the vmemmap area before the corresponding top-level entries were synced. At that time, the issue was believed to be triggered only when struct page was enlarged for debugging purposes, and the patch did not get further updates. It turns out that current approach of relying on each arch to handle the page table sync manually is fragile because 1) it's easy to forget to sync the top level page table, and 2) it's also easy to overlook that the kernel should not access the vmemmap and direct mapping areas before the sync. # The solution: Make page table sync more code robust and harder to miss To address this, Dave Hansen suggested [3] [4] introducing {pgd,p4d}_populate_kernel() for updating kernel portion of the page tables and allow each architecture to explicitly perform synchronization when installing top-level entries. With this approach, we no longer need to worry about missing the sync step, reducing the risk of future regressions. The new interface reuses existing ARCH_PAGE_TABLE_SYNC_MASK, PGTBL_P*D_MODIFIED and arch_sync_kernel_mappings() facility used by vmalloc and ioremap to synchronize page tables. pgd_populate_kernel() looks like this: static inline void pgd_populate_kernel(unsigned long addr, pgd_t *pgd, p4d_t *p4d) { pgd_populate(&init_mm, pgd, p4d); if (ARCH_PAGE_TABLE_SYNC_MASK & PGTBL_PGD_MODIFIED) arch_sync_kernel_mappings(addr, addr); } It is worth noting that vmalloc() and apply_to_range() carefully synchronizes page tables by calling p*d_alloc_track() and arch_sync_kernel_mappings(), and thus they are not affected by ---truncated---

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: NVD-CWE-noinfo

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 8d400913c231bd1da74067255816453f96cd35b0 732e62212f49d549c91071b4da7942ee3058f7a2 git Not specified
CNA Linux Linux affected 8d400913c231bd1da74067255816453f96cd35b0 eceb44e1f94bd641b2a4e8c09b64c797c4eabc15 git Not specified
CNA Linux Linux affected 8d400913c231bd1da74067255816453f96cd35b0 6797a8b3f71b2cb558b8771a03450dc3e004e453 git Not specified
CNA Linux Linux affected 8d400913c231bd1da74067255816453f96cd35b0 4f7537772011fad832f83d6848f8eab282545bef git Not specified
CNA Linux Linux affected 8d400913c231bd1da74067255816453f96cd35b0 469f9d22751472b81eaaf8a27fcdb5a70741c342 git Not specified
CNA Linux Linux affected 8d400913c231bd1da74067255816453f96cd35b0 7cc183f2e67d19b03ee5c13a6664b8c6cc37ff9d git Not specified
CNA Linux Linux affected 5.13 Not specified
CNA Linux Linux unaffected 5.13 semver Not specified
CNA Linux Linux unaffected 5.15.192 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.151 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.105 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.46 6.12.* semver Not specified
CNA Linux Linux unaffected 6.16.6 6.16.* semver Not specified
CNA Linux Linux unaffected 6.17 * original_commit_for_fix Not specified
ADP Siemens SIMATIC CN 4100 affected V5.0 custom Not specified

References

ReferenceSourceLinkTags
lists.debian.org/debian-lts-announce/2025/10/msg00008.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Mailing List, Third Party Advisory
git.kernel.org/stable/c/469f9d22751472b81eaaf8a27fcdb5a70741c342 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/732e62212f49d549c91071b4da7942ee3058f7a2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/6797a8b3f71b2cb558b8771a03450dc3e004e453 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
cert-portal.siemens.com/productcert/html/ssa-032379.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/4f7537772011fad832f83d6848f8eab282545bef 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/7cc183f2e67d19b03ee5c13a6664b8c6cc37ff9d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/eceb44e1f94bd641b2a4e8c09b64c797c4eabc15 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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