Linux Kernel up to 6.1.10 find_pmd_or_thp_or_none state issue

Summaryinfo

A vulnerability classified as problematic was found in Linux Kernel up to 6.1.10. The affected element is the function find_pmd_or_thp_or_none. Executing a manipulation can lead to state issue. The identification of this vulnerability is CVE-2023-52934. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.1.10. It has been declared as problematic. This vulnerability affects the function find_pmd_or_thp_or_none. The manipulation with an unknown input leads to a state issue vulnerability. The CWE definition for the vulnerability is CWE-371. The impact remains unknown. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: mm/MADV_COLLAPSE: catch !none !huge !bad pmd lookups In commit 34488399fa08 ("mm/madvise: add file and shmem support to MADV_COLLAPSE") we make the following change to find_pmd_or_thp_or_none(): - if (!pmd_present(pmde)) - return SCAN_PMD_NULL; + if (pmd_none(pmde)) + return SCAN_PMD_NONE; This was for-use by MADV_COLLAPSE file/shmem codepaths, where MADV_COLLAPSE might identify a pte-mapped hugepage, only to have khugepaged race-in, free the pte table, and clear the pmd. Such codepaths include: A) If we find a suitably-aligned compound page of order HPAGE_PMD_ORDER already in the pagecache. B) In retract_page_tables(), if we fail to grab mmap_lock for the target mm/address. In these cases, collapse_pte_mapped_thp() really does expect a none (not just !present) pmd, and we want to suitably identify that case separate from the case where no pmd is found, or it's a bad-pmd (of course, many things could happen once we drop mmap_lock, and the pmd could plausibly undergo multiple transitions due to intervening fault, split, etc). Regardless, the code is prepared install a huge-pmd only when the existing pmd entry is either a genuine pte-table-mapping-pmd, or the none-pmd. However, the commit introduces a logical hole; namely, that we've allowed !none- && !huge- && !bad-pmds to be classified as genuine pte-table-mapping-pmds. One such example that could leak through are swap entries. The pmd values aren't checked again before use in pte_offset_map_lock(), which is expecting nothing less than a genuine pte-table-mapping-pmd. We want to put back the !pmd_present() check (below the pmd_none() check), but need to be careful to deal with subtleties in pmd transitions and treatments by various arch. The issue is that __split_huge_pmd_locked() temporarily clears the present bit (or otherwise marks the entry as invalid), but pmd_present() and pmd_trans_huge() still need to return true while the pmd is in this transitory state. For example, x86's pmd_present() also checks the _PAGE_PSE , riscv's version also checks the _PAGE_LEAF bit, and arm64 also checks a PMD_PRESENT_INVALID bit. Covering all 4 cases for x86 (all checks done on the same pmd value): 1) pmd_present() && pmd_trans_huge() All we actually know here is that the PSE bit is set. Either: a) We aren't racing with __split_huge_page(), and PRESENT or PROTNONE is set. => huge-pmd b) We are currently racing with __split_huge_page(). The danger here is that we proceed as-if we have a huge-pmd, but really we are looking at a pte-mapping-pmd. So, what is the risk of this danger? The only relevant path is: madvise_collapse() -> collapse_pte_mapped_thp() Where we might just incorrectly report back "success", when really the memory isn't pmd-backed. This is fine, since split could happen immediately after (actually) successful madvise_collapse(). So, it should be safe to just assume huge-pmd here. 2) pmd_present() && !pmd_trans_huge() Either: a) PSE not set and either PRESENT or PROTNONE is. => pte-table-mapping pmd (or PROT_NONE) b) devmap. This routine can be called immediately after unlocking/locking mmap_lock -- or called with no locks held (see khugepaged_scan_mm_slot()), so previous VMA checks have since been invalidated. 3) !pmd_present() && pmd_trans_huge() Not possible. 4) !pmd_present() && !pmd_trans_huge() Neither PRESENT nor PROTNONE set => not present I've checked all archs that implement pmd_trans_huge() (arm64, riscv, powerpc, longarch, x86, mips, s390) and this logic roughly translates (though devmap treatment is unique to x86 and powerpc, and (3) doesn't necessarily hold in general -- but that doesn't matter since !pmd_present() always takes failure path). Also, add a comment above find_pmd_or_thp_or_none() ---truncated---

The advisory is available at git.kernel.org. This vulnerability was named CVE-2023-52934 since 08/21/2024. The exploitation appears to be difficult. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 12/07/2025).

Upgrading to version 6.1.11 eliminates this vulnerability. Applying the patch 96aaaf8666010a39430cecf8a65c7ce2908a030f/edb5d0cf5525357652aff6eacd9850b8ced07143 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2025-0649). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Affected

• Google Container-Optimized OS
• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• Dell Avamar
• Open Source Linux Kernel
• SolarWinds Security Event Manager
• Dell NetWorker
• Dell Secure Connect Gateway

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.1.0
• 6.1.1
• 6.1.2
• 6.1.3
• 6.1.4
• 6.1.5
• 6.1.6
• 6.1.7
• 6.1.8
• 6.1.9
• 6.1.10

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

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CPE 2.2info

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Exploitinginfo

Threat Intelligenceinfo

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Timelineinfo

Sourcesinfo

Entryinfo

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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