[CVE-2026-98475][MODERATE 7.0] s390/cmf: Fix virtual vs physical address confusion

[CVE-2026-98475][MODERATE 7.0] s390/cmf: Fix virtual vs physical address confusion

[AL-KERNEL]

CVE: CVE-2026-98475
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: s390/cmf: Fix virtual vs physical address confusion
Commit: b11f369be31ea11c746833e4d3ad51dcd6b5fa2b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b11f369be31ea11c746833e4d3ad51dcd6b5fa2b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98475
Analysis date: Mon, 19 Oct 2026 06:00:04 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
An s390 address-domain conversion error can cause channel firmware to use a kernel virtual measurement-block address as an absolute DMA destination, potentially corrupting unintended physical memory and crashing the host.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98475 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98475

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-98475	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98475 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H';CWE-704;CWE-681;*CWE-787;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '6.4';DESCR 'An address space confusion in s390 channel measurement handling can pass a virtual measurement block address to firmware as an absolute DMA address. On kernels built with CONFIG_RANDOMIZE_IDENTITY_BASE, firmware may therefore store extended channel measurement data at an unintended physical address. Depending on firmware address validation and the resulting location, this may cause measurement failure, corruption of unrelated physical memory, a kernel crash, or loss of system availability. The issue is local, specific to affected s390 configurations, and is not directly network reachable. For the CVSS the PR:H is selected because activating or configuring channel measurement blocks normally requires administrative control over the channel subsystem. The base score represents limited integrity impact and high availability impact from a wrong firmware write. The paranoid score treats the unintended physical memory write as a potential strong kernel memory corruption primitive, although reliable attacker control over the destination and contents is not established. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 6.4 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were KP and FD specialist checks stage MODERATE_KPANIC to MODERATE because KP specialist did not establish a qualifying panic. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 3.7 and ActionableScore 1 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	OOB SIMPLEFIX LINUS MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

## 1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 4
* Paranoid score: 4
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* +1 Constrained kernel overwrite. A kernel virtual address is supplied as an absolute DMA address, so firmware can store measurement data at the wrong physical destination.
* +1 Privileged device-management corruption path. The malformed `schib_config.mba` value is an active DMA descriptor consumed by privileged channel-subsystem firmware.
* +1 Integrity plausible. If the translated value identifies valid but unintended physical memory, firmware can overwrite memory outside the allocated measurement block.

Paranoid-only signal:

* +1 Strong DoS plausible. An unintended firmware write into host physical memory can realistically corrupt kernel data and cause a kernel crash, although the patch does not document a specific panic trace.

No negative points:

* The s390 architecture, extended measurement format, and `CONFIG_RANDOMIZE_IDENTITY_BASE=y` are required, but rarity and practical trigger difficulty are not sufficiently established to apply a configuration or hardware penalty.
* Host-admin privilege is not proven by the supplied call sites, so no privilege penalty is applied.

Important non-awarded signals:

* No attacker-controlled destination or payload is demonstrated.
* No arbitrary or directed write is established.
* No controlled reclaim, UAF, disclosure, authorization bypass, or privilege escalation is established.
* No remote, guest, namespace, or delegated-interface trigger is shown.
* V33 does not apply because attacker influence over the active descriptor and a credible guest or namespace trust boundary are not established.
* B5-R does not apply because there is no retry-accumulated index or heap OOB sequence.
* B3-PENDING does not apply because no shared or file-backed storage modification is shown.
* B4-PENDING does not apply because no authorization decision is involved.

## 3. Reachability analysis

The affected path exists only on s390 systems using extended-format channel measurement data with `CONFIG_RANDOMIZE_IDENTITY_BASE=y`. The supplied patch does not show the userspace caller, sysfs permissions, or capability check needed to activate or reconfigure measurement blocks. Consequently, the complete attacker privilege requirement remains unknown rather than being assumed to require host administration.

The channel subsystem controls physical s390 devices and is not an attacker-created user or network namespace facility, so namespace-scoped privilege is not supported. There is no race and no network-reachable input. The required address mismatch is deterministic once the affected configuration and measurement mode are active.

## 4. Primitive and severity interpretation

The exact primitive is an incorrect address-domain conversion. `set_schib()` places a kernel virtual address directly into a field interpreted by firmware as an absolute DMA address. Firmware subsequently uses that value as the destination for extended channel measurement data.

This is an active structured DMA descriptor consumed by firmware, not a UAF or stale object. The resulting write is constrained because the address is kernel-derived and the measurement payload is firmware-generated. It is nevertheless stronger than passive metadata corruption because an unintended physical-memory write may occur.

The demonstrated defect is a wrong firmware write destination. Corruption of unrelated host memory and a crash are credible consequences, but reliable target selection, arbitrary payload control, disclosure, LPE, and a security-boundary crossing are not established. It is therefore CLASS_B rather than CLASS_A.

`ImportantCandidate=NO` because meaningful attacker control and below-host-admin reachability are unresolved. `AutoDowngradeAllowed=NO` because automatically treating an active firmware write to an unintended physical address as an ordinary harmless device error could discard a real host-memory integrity risk. Architecture-specific manual analysis should determine the actual address produced, firmware validation behavior, measurement write size, and activation permissions.

## 5. One-sentence report phrase

An s390 address-domain conversion error can cause channel firmware to use a kernel virtual measurement-block address as an absolute DMA destination, potentially corrupting unintended physical memory and crashing the host.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Confirm the `set_schib()` callers and permissions, the resulting physical destination under randomized identity mapping, firmware address validation, and whether the write can overlap active kernel memory.

## 7. Call-site confidence

Call-site confidence: medium

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

Patch: s390/cmf: Fix virtual vs physical address confusion
Commit: b11f369be31ea11c746833e4d3ad51dcd6b5fa2b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b11f369be31ea11c746833e4d3ad51dcd6b5fa2b

Commit description:

The measurement block address is an absolute address. Define the
associated schib_config and schib fields as dma64_t to enable automatic
detection of incorrect assignments. Also add the missing virt_to_dma64()
translation.

Without this fix, a wrong address will be used by firmware when storing
extended format channel measurement data on kernels built with
CONFIG_RANDOMIZE_IDENTITY_BASE=y.

Fixes: 14edd0d ("s390/cmf: fix virtual vs physical address confusion")
Cc: stable@vger.kernel.org
Signed-off-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/s390/cio/cio.h
  drivers/s390/cio/cmf.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=b11f369be31ea11c746833e4d3ad51dcd6b5fa2b

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

The original Linux kernel CVE announcement for CVE-2026-98475 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98475

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:H/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: 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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).