[CVE-2026-68172][MODERATE REGULAR] arm64: make huge_ptep_get handled unaligned addresses

[CVE-2026-68172][MODERATE REGULAR] arm64: make huge_ptep_get handled unaligned addresses

[AL-KERNEL]

CVE: CVE-2026-68172
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: arm64: make huge_ptep_get handled unaligned addresses
Commit: 9cd4b1a52eff330798d668c1775f8bc450776280
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9cd4b1a52eff330798d668c1775f8bc450776280
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68172
Analysis date: Mon, 10 Aug 2026 13:39:10 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
An arm64 hugetlb address-alignment bug in huge_ptep_get() can misclassify contpmd mappings as contpte mappings and walk past the expected PTE table, allowing a local process on affected 16K-page hugetlb systems to trigger a kernel panic.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68172 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68172

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE REGULAR
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-68172	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-125;CWE-823;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'An arm64 hugetlb bug can make huge_ptep_get() misclassify a contpmd mapped hugetlb folio as contpte when the supplied virtual address points into the middle of the mapping. This can make the kernel collect A/D state from too many entries and may walk past the end of the PTE table, dereferencing an out of range ptep in the linear map. The most likely impact is a local denial of service via kernel panic on affected arm64 systems with the relevant hugetlb and 16K page size conditions. For the CVSS the PR:L is used because a local user or local process is needed to drive the hugetlb or pagemap related path, while full administrator privileges are not necessarily required when huge pages and access policy are already available. The issue is not network reachable. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives. Impact is at least local denial of service and in worst case may allow limited confidentiality or integrity impact due to out of range page table metadata reads, but the patch does not show a controlled write primitive or a strong privilege escalation path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4)  SKIP CVE-2026-68172 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 29cb80519689706387bde47000dbb2ed91143063 YES  NO NO unknown 	MAYBE	OOB DANGER HARDWARE MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  The likely call paths include pagemap_hugetlb_range() and page_mapped_in_vma(). A local process may be able to trigger the path if hugetlb mappings are available and the relevant procfs or memory-management path is reachable.

* Memory corruption, Weak/indirect corruption candidate: +1
  The patch describes a misclassified contpmd/contpte mapping that can make the kernel walk beyond the expected PTE table and dereference a garbage ptep pointer. This is an invalid kernel pointer dereference / out-of-range page-table metadata access, but not a demonstrated write primitive.

* Reliable kernel crash / strong DoS: +1
  The commit explicitly states that the kernel may dereference a VA not mapped into the kernel page tables and cause a kernel panic.

* Availability impact realistic: +1, paranoid only
  The failure mode is a host-wide kernel panic. I count this in the paranoid score because the crash is system-wide, but avoid heavy double-counting in the conservative score.

Subtracted signals:

* Rare AND difficult-to-reach subsystem/configuration: -1
  The issue appears specific to arm64 hugetlb contiguous mappings, especially systems where CONT_PTES != CONT_PMDS, meaning 16K page size. It also requires a relevant hugepage mapping and an unaligned address into the middle of the mapping.

Not awarded:

* Remote reachable / network-triggerable: +0
  No network path is indicated.

* Strong LPE plausibility: +0
  The patch does not show attacker-controlled reclaim, overwrite, callback control, type confusion, refcount takeover, or arbitrary write.

* Confidentiality / integrity impact: +0 conservative
  The bug may read out-of-range page-table-related memory internally, but there is no clear user-visible disclosure path or controlled modification primitive.

## 3. Reachability analysis

The bug is local. It requires an affected arm64 configuration, relevant hugetlb contiguous mappings, and a caller that passes an address inside the mapping rather than aligned to the base. The commit names pagemap_hugetlb_range() and page_mapped_in_vma() as example callers.

Namespaces and containers may matter only if the environment exposes hugetlb usage or pagemap-like inspection paths to less privileged workloads. In typical hardened deployments, hugepage availability and pagemap usefulness may be restricted, which reduces practical reachability.

This is not default network exposure. Realistic exploitation is most likely a local DoS attempt on a specific arm64 16K-page configuration with hugetlb enabled and usable.

## 4. Severity interpretation

This behaves more like a Borderline / actionable Moderate candidate than an Important-class issue.

Theoretical risk exists because the kernel can walk past the expected PTE table and dereference a garbage ptep pointer in the linear map. However, the demonstrated primitive is an invalid read / invalid pointer dereference leading to panic, not a controlled write, UAF reclaim, type confusion, or privilege-escalation primitive.

The main practical impact is local kernel panic. Manual review is still recommended because the bug is in architecture MM / hugetlb page-table handling, and the failure mode involves out-of-range page-table metadata access rather than a simple WARN or resource leak.

## 5. One-sentence report phrase

An arm64 hugetlb address-alignment bug in huge_ptep_get() can misclassify contpmd mappings as contpte mappings and walk past the expected PTE table, allowing a local process on affected 16K-page hugetlb systems to trigger a kernel panic.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the bug is not a strong Important candidate by itself, but it is an MM/page-table invalid-access issue with a documented kernel panic path, so it should not be blindly auto-closed as a trivial DoS without confirming affected arm64 configurations and reachable call paths.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: arm64: make huge_ptep_get handled unaligned addresses
Commit: 9cd4b1a52eff330798d668c1775f8bc450776280
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9cd4b1a52eff330798d668c1775f8bc450776280

Commit description:

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.

Fixes: 29cb805 ("arm64: hugetlb: Cleanup huge_pte size discovery mechanisms")
Cc: stable@vger.kernel.org
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/arm64/mm/hugetlbpage.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9cd4b1a52eff330798d668c1775f8bc450776280

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DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-68172 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68172

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 3
  Paranoid ActionableScore: 4

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).