In the Linux kernel, the following vulnerability has been resolved:

mm: huge_memory: fix misused mapping_large_folio_support() for anon folios

When I did a large folios split test, a WARNING "[ 5059.122759][ T166]
Cannot split file folio to non-0 order" was triggered. But the test cases
are only for anonmous folios. while mapping_large_folio_support() is only
reasonable for page cache folios.

In split_huge_page_to_list_to_order(), the folio passed to
mapping_large_folio_support() maybe anonmous folio. The folio_test_anon()
check is missing. So the split of the anonmous THP is failed. This is
also the same for shmem_mapping(). We'd better add a check for both. But
the shmem_mapping() in __split_huge_page() is not involved, as for
anonmous folios, the end parameter is set to -1, so (head[i].index >= end)
is always false. shmem_mapping() is not called.

Also add a VM_WARN_ON_ONCE() in mapping_large_folio_support() for anon
mapping, So we can detect the wrong use more easily.

THP folios maybe exist in the pagecache even the file system doesn't
support large folio, it is because when CONFIG_TRANSPARENT_HUGEPAGE is
enabled, khugepaged will try to collapse read-only file-backed pages to
THP. But the mapping does not actually support multi order large folios
properly.

Using /sys/kernel/debug/split_huge_pages to verify this, with this patch,
large anon THP is successfully split and the warning is ceased.
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Wed, 11 Sep 2024 13:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2025-05-04T09:18:36.796Z

Reserved: 2024-07-12T12:17:45.591Z

Link: CVE-2024-40950

cve-icon Vulnrichment

Updated: 2024-08-02T04:39:55.883Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2024-07-12T13:15:17.353

Modified: 2024-11-21T09:31:55.947

Link: CVE-2024-40950

cve-icon Redhat

Severity : Moderate

Publid Date: 2024-07-12T00:00:00Z

Links: CVE-2024-40950 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2025-07-13T11:31:59Z