From: AL-KERNEL <[email protected]>
To: [email protected]
Subject: [CVE-2026-93217][LOW] mm/madvise: skip device-private PMDs in cold and pageout walks
Date: Thu, 24 Sep 2026 12:41:36 -0400 [thread overview]
Message-ID: <[email protected]> (raw)
CVE: CVE-2026-93217
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm/madvise: skip device-private PMDs in cold and pageout walks
Commit: 5c0d7b658cda62cd17cb3652783386d5608030ef
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c0d7b658cda62cd17cb3652783386d5608030ef
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93217
Analysis date: Thu, 24 Sep 2026 12:41:36 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93217 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93217
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: LOW
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-93217 LOW https://www.kernelcve.org/list/?q=CVE-2026-93217 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-617;CWE-667;BEST CVSS score: '4.7';DESCR 'A race in madvise_cold_or_pageout_pte_range can occur when an HMM based GPU driver converts a transparent huge PMD into a device private entry after the initial PMD check but before the PMD lock is acquired. The valid device private entry can then reach a VM_BUG_ON that accepts only migration entries, causing a kernel panic and local denial of service on affected debug configurations. For the CVSS the PR:L is selected because an unprivileged local process can normally call MADV_COLD or MADV_PAGEOUT for its own eligible mapping, while the concurrent HMM migration and required GPU memory configuration are external prerequisites rather than attacker privileges. AC:H reflects the required race window and the dependency on device private THP support and an HMM capable driver. The issue is not network reachable. Impact is limited to availability because the locked non present branch exits through huge_unlock before pmd_folio is called, and the analyzed path provides no UAF, out of bounds access, information disclosure, or write primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) SKIP CVE-2026-93217 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE SIMPLEFIX RACE HARDWARE MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
Positive signals:
* +1 Local unprivileged trigger. An ordinary process can invoke MADV_COLD or MADV_PAGEOUT on its own eligible mapping without host-admin privilege.
* +1 Reliable kernel crash. A device-private PMD can reach VM_BUG_ON and panic an affected kernel configuration.
Negative signals:
* -1 Hard timing requirement. The trigger requires migration to replace the PMD after the initial pmd_trans_huge check but before acquisition of the PMD lock.
* -1 Rare and difficult configuration combination. The fatal path requires device-private PMD support, an HMM-capable GPU driver, suitable GPU-managed memory, and a kernel configuration where VM_BUG_ON is active.
Not awarded:
* No UAF or post-lifetime object use is established.
* No OOB access, arbitrary write, controlled corruption, or controlled reclaim is established.
* No confidentiality or integrity signal is awarded.
* No remote reachability is established.
* No additional Availability point is awarded because the kernel panic is already counted.
* No active-state retirement, reverse-mapping, ownership, or translation-domain bypass is shown.
* The paranoid score is not increased because stronger consequences would require a new, unsupported memory-corruption primitive.
3. Reachability analysis
The evaluated attacker is an ordinary local process using MADV_COLD or MADV_PAGEOUT on its own mapping while an HMM-based GPU driver migrates the relevant memory to a device-private PMD. The madvise operation itself requires no capability, so host-admin-equivalent privilege is not required.
No namespace capability is involved. Prior host configuration must provide a compatible HMM GPU driver, device-private THP support, and GPU-managed memory. The panic additionally depends on a configuration where VM_BUG_ON is active. The attacker can repeat madvise calls, but the critical PMD conversion must occur within the narrow interval before the PMD lock is acquired, and complete control over that interleaving is not established.
4. Primitive and severity interpretation
The exact primitive is a reachable invalid assertion caused by a race between an unlocked preliminary PMD observation and a later locked examination of the updated PMD. A valid device-private PMD is incorrectly rejected as an impossible non-present state.
This is not a stale object or lifetime violation. There is no first release, dangling reference, second refcount mutation, or repeated-release condition. The branch exits through huge_unlock before pmd_folio is called, so the supplied path does not continue into an invalid folio dereference.
The demonstrated consequence is a configuration-dependent kernel panic and local denial of service. Memory corruption, information disclosure, privilege escalation, and persistent integrity effects are unsupported. The issue is therefore CLASS_C rather than CLASS_B or CLASS_A.
ImportantCandidate is NO because there is no independently useful corruption or boundary-bypass primitive beyond the assertion-triggered crash. AutoDowngradeAllowed is YES because preserving this issue for Important-grade exploitation review would require unsupported assumptions about later memory use.
5. One-sentence report phrase
A local process using MADV_COLD or MADV_PAGEOUT can race with HMM GPU migration and trigger a fatal assertion on a valid device-private PMD, causing a configuration-dependent kernel panic without an established memory-corruption primitive.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch establishes a constrained assertion-based local DoS, and the affected branch unlocks and exits before performing further PMD or folio processing.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: mm/madvise: skip device-private PMDs in cold and pageout walks
Commit: 5c0d7b658cda62cd17cb3652783386d5608030ef
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c0d7b658cda62cd17cb3652783386d5608030ef
Commit description:
madvise_cold_or_pageout_pte_range() takes pmd_trans_huge_lock(), whose
pmd_is_huge() check returns true for a device-private PMD. The subsequent
!pmd_present() branch has a VM_BUG_ON() asserting migration is the only
allowed non-present case; a device-private PMD trips it.
Skip device-private PMDs in that non-present branch and continue to
huge_unlock before calling pmd_folio(). Downgrade the check to
VM_WARN_ON_ONCE() so an unexpected PMD softleaf logs a warning rather than
panicking. Drop the thp_migration_supported() guard: it expands to
IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_SOFTLEAF), and both
pmd_is_migration_entry() and pmd_is_device_private_entry() already return
false when that config is not selected, so the guard suppresses only the
case where the warning would already be silent.
Potential trigger: an HMM-based GPU driver races with
madvise(MADV_COLD)/MADV_PAGEOUT: pmd_trans_huge(*pmd) reads true, then
migrate_vma_pages() flips the PMD to a device-private entry before the PMD
lock is acquired.
Link: https://lore.kernel.org/[email protected]
Fixes: 368076f ("mm/huge_memory: add device-private THP support to PMD operations")
Signed-off-by: Usama Arif <[email protected]>
Reported-by: sashiko-bot <[email protected]>
Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=6
Reviewed-by: Joshua Hahn <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Reviewed-by: Balbir Singh <[email protected]>
Reviewed-by: Gregory Price <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: David Hildenbrand (Arm) <[email protected]>
Cc: Dev Jain <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Lance Yang <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Nico Pache <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
mm/madvise.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=5c0d7b658cda62cd17cb3652783386d5608030ef
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-93217 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93217
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: Not available
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: unknown
Paranoid ActionableScore: 0
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
reply other threads:[~2026-09-24 16:41 UTC|newest]
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