CVE-2026-68172 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
arm64: make huge_ptep_get handled unaligned addresses
huge_ptep_get() can be handed a virtual address pointing to the middle of a contpmd/contpte mapped hugetlb folio (examples of callers are pagemap_hugetlb_range, page_mapped_in_vma).
The arm64 helper rewalks the pgtables in find_num_contig to answer whether the huge pte we have maps a contpmd or a contpte hugetlb folio, and returns CONT_PMDS or CONT_PTES, so that it can collect a/d bits over the contiguous ptes. We can falsely return CONT_PTES instead of CONT_PMDS if the addr is not aligned. On systems where CONT_PTES != CONT_PMDS (meaning page size is 16K), we could collect excess A/D bit state, meaning extra work for the kernel. Even worse, we may iterate beyond the PTE table and dereference a garbage ptep pointer to access physical memory we don't own. Since the ptep pointer is a linear map address, we may run off the end of the linear map or into a hole, dereference a VA not mapped into the kernel pgtables and cause kernel panic.
Fix this by aligning the pmdp pointer down to a contpmd base before checking equality with the passed huge pte pointer, to correctly answer whether the huge pte is the base of a contpmd block.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability identified in the Linux kernel's arm64 architecture relates to improper handling of unaligned memory addresses within the huge page table entry processing mechanism. This flaw exists in the huge_ptep_get() function which serves as an interface for accessing huge page table entries when dealing with hugetlb folios that are mapped using contiguous page table entries. The specific issue occurs when the function receives a virtual address pointing to the middle of a contpmd or contpte mapped hugetlb folio, rather than at the beginning of such mappings.
The technical implementation of this vulnerability stems from the arm64 helper function find_num_contig which rewalks page tables to determine whether the current huge page table entry maps a contiguous pmd (page middle directory) or contiguous pte (page table entry) hugetlb folio. This determination is crucial for collecting access and dirty bits across contiguous page table entries. The flaw manifests when the function fails to properly align the address before performing equality checks, causing it to incorrectly return CONT_PTES instead of CONT_PMDS when dealing with unaligned addresses. This misclassification occurs because the function does not account for the fact that on systems where contpte values differ from contpmd values (specifically those using 16K page sizes), the address alignment affects the proper identification of the mapping type.
The operational impact of this vulnerability is significant and potentially catastrophic for kernel stability and security. When the system incorrectly identifies a huge pte as being part of a contpte mapping rather than a contpmd mapping, it can lead to collecting excessive A/D (access and dirty) bit state information, resulting in unnecessary kernel processing overhead. More critically, this misalignment can cause the kernel to iterate beyond the legitimate PTE table boundaries and attempt to dereference garbage ptep pointers. Since these pointers are linear map addresses, such errors may result in accessing physical memory locations that the kernel does not own, potentially leading to kernel panics when attempting to access virtual addresses that are not properly mapped into the kernel's page tables or when running off the end of the linear mapping region.
This vulnerability directly relates to CWE-129 and CWE-787 within the Common Weakness Enumeration framework, representing issues related to improper input validation and out-of-bounds memory access. The flaw also aligns with ATT&CK techniques focusing on privilege escalation through kernel exploitation, specifically targeting kernel memory corruption and information disclosure via improper memory management. The fix implemented addresses this by ensuring that the pmdp pointer is properly aligned down to a contpmd base before performing equality comparisons with the passed huge pte pointer, thereby correctly identifying whether the huge pte represents the base of a contiguous pmd block rather than incorrectly classifying it based on an unaligned address. This alignment ensures proper boundary checking and prevents both performance degradation through unnecessary processing and potential security exploits through unauthorized memory access attempts.