* [CVE-2026-90383][MODERATE 7.0] misc: sgi-gru: remove interrupt-context page-table walks [ Upstream
@ 2026-09-18 0:12 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-18 0:12 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90383
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: misc: sgi-gru: remove interrupt-context page-table walks [ Upstream
Commit: 877423f595b60f8fe7c18b64a5d283d9e1732a13
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=877423f595b60f8fe7c18b64a5d283d9e1732a13
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90383
Analysis date: Thu, 17 Sep 2026 20:12:58 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90383 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90383
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 7.0
Manual review required: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-90383 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90383 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:H/I:H/A:H';CWE-362;CWE-667;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'The SGI GRU TLB miss handler could walk user process page tables in interrupt context without holding page-table locks and without taking a reference on the mapped page. A local user with access to GRU functionality may be able to race address translation against mapping changes and cause a stale physical translation to be used by the device. For the CVSS the PR:L value is used because reliable triggering requires local user execution and access to the GRU user interface, but not full administrative privileges. The issue is not network reachable and is highly hardware specific. Impact is at least local denial of service via crash or invalid device translation. In the worst case, stale page-table state may allow confidentiality or integrity impact through access to reused memory and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES READ OOB LOCK DANGER SIMPLEFIX DMAorINTERRUPT KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 5
* Conservative floor/cap: RealUAF floor applied. 1 -> 4
* Paranoid floor/cap: RealUAF floor 5 applied due stale physical translation surface and local GRU user reachability. 3 -> 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2 Real UAF / lifetime violation. The GRU interrupt handler walked user page tables without page-table locks and without taking a reference on the mapped page. This directly implies a stale page / stale physical translation risk.
* +1 Local below-host-admin reachability. Supplied context indicates a local user with access to GRU functionality may trigger GRU faults and influence the user mappings involved.
* +1 Weak exploitation concern. A stale PFN may be installed into GRU translation state and later used by the device, which is more security-relevant than a simple NULL dereference.
* -1 Hard timing / interrupt-context race. The problematic path depends on interrupt fault handling racing against user mapping changes without proper page-table synchronization.
* -2 Rare hardware. SGI GRU is highly hardware-specific and not broadly deployed.
Paranoid additional signal:
* +1 Strong DoS / invalid translation concern. A stale or invalid device translation can plausibly cause kernel/device fault or system instability.
* No controlled reclaim was demonstrated.
* No arbitrary kernel read/write was demonstrated.
* No callback or function-pointer control was demonstrated.
* No concrete repeated release/refcount mutation exists.
* No extra availability point was awarded beyond the same crash/invalid-translation consequence.
* C/I were not scored as proven impacts, but stale physical translation creates enough unresolved confidentiality/integrity concern for manual review.
Repeated release/refcount check:
* First release can end lifetime: not applicable.
* Exact same reference survives to second put/free: not established.
* Second lifetime/refcount mutation: not established.
* Concrete repeated release/refcount +1: not awarded.
* Paranoid repeated-refcount +1: not awarded.
* FLOOR 5: applied in paranoid due meaningful stale page / device translation surface, not due repeated release.
3. Reachability analysis
The evaluated attacker is a local user with access to the SGI GRU user interface. Host administrator privilege is not positively required by the supplied context, so HostAdminRequired=NO. This is not a namespace-scoped capability issue, so NamespaceScopedPrivilege=NO.
The issue is not network reachable. A prior hardware/configuration prerequisite exists because the system must have SGI GRU hardware and the driver path available. This is a strong deployment limiter.
The race is timing-sensitive because the removed path attempted translation in interrupt context while user mappings could change. However, the attacker can plausibly influence the relevant user virtual address mappings and trigger GRU faults repeatedly if they have access to the device.
4. Primitive and severity interpretation
The primitive is an unsafe interrupt-context user page-table walk without page-table locks or page references. This can yield a stale physical address and install it into GRU translation state. This is best treated as CLASS_B lifetime / stale translation corruption rather than CLASS_A, because controlled reclaim, directed write, or a demonstrated privilege-escalation chain is not established.
The stale storage is a page / physical translation rather than an ordinary fixed cleanup pointer. The stale use is not merely a destructor-time dereference. It may affect active device translation state.
Demonstrated consequence is invalid translation and likely crash or device/system instability. Speculative consequence is access to reused memory through stale translation, which could affect confidentiality or integrity, but this is not proven enough to score as CLASS_A.
ImportantCandidate=YES because the stale page-table / page-reference primitive has unresolved exploitation implications beyond a simple warning. AutoDowngradeAllowed=NO because automatic closure would risk losing a concrete lifetime/translation primitive requiring manual review.
Likely operational severity is Actionable Moderate, with Strong Important review needed only if additional evidence shows controlled reuse, cross-process memory access, DMA corruption, or privilege escalation.
5. One-sentence report phrase
The SGI GRU TLB miss handler could walk user page tables in interrupt context without page-table locks or page references, allowing a local GRU user to race mapping changes and create stale device translations that may cause DoS and require manual review for possible memory access impact.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: this is not a simple crash-only warning. The patch removes an unsafe interrupt-context page-table walker that could create stale physical translations without holding page references.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: misc: sgi-gru: remove interrupt-context page-table walks [ Upstream
Commit: 877423f595b60f8fe7c18b64a5d283d9e1732a13
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=877423f595b60f8fe7c18b64a5d283d9e1732a13
Changed files:
drivers/misc/sgi-gru/grufault.c
drivers/misc/sgi-gru/gruprocfs.c
drivers/misc/sgi-gru/grutables.h
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=877423f595b60f8fe7c18b64a5d283d9e1732a13
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90383 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90383
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:L/I:L/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
The Best / paranoid CVSS score: 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: 4
Paranoid ActionableScore: 5
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: YES
Published priority for this report (same as in Subject): MODERATE 7.0
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).
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