[CVE-2026-90315][IMPORTANT] PCI/sysfs: Add lockdown checks to legacy I/O and memory handlers [ Upstream

[CVE-2026-90315][IMPORTANT] PCI/sysfs: Add lockdown checks to legacy I/O and memory handlers [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90315
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: PCI/sysfs: Add lockdown checks to legacy I/O and memory handlers [ Upstream
Commit: cd07aef510ac6a2873e01f9ddddc5492490b0067
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cd07aef510ac6a2873e01f9ddddc5492490b0067
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90315
Analysis date: Fri, 18 Sep 2026 00:25:14 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-90315 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90315

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: IMPORTANT
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-2026-90315	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-90315 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:H/I:H/A:H';CWE-693;CWE-284;CWE-269;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7';DESCR 'PCI sysfs legacy I/O and legacy memory handlers lacked LOCKDOWN_PCI_ACCESS checks while the kernel was in lockdown mode. A local attacker with root level access to these sysfs files could still write I/O ports or mmap legacy PCI memory and I/O spaces, bypassing the lockdown policy that is intended to prevent direct hardware access. For the CVSS the PR:L in the paranoid score reflects environments where a reduced capability root, container root, or delegated service account can access host PCI sysfs paths but is otherwise constrained by lockdown. The issue is not network reachable. Impact can include lockdown bypass with high integrity risk and possible confidentiality or availability impact if hardware access is used to DMA or otherwise tamper with kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 6)	YES	READ HARDWARE LINUS  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	YES	NO	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=7
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 7
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate**::

No floor or cap changed the score.

2. Signal breakdown

Conservative signals:

* +2 Concrete authorization decision bypass. The legacy PCI sysfs I/O and memory handlers skipped `security_locked_down(LOCKDOWN_PCI_ACCESS)` while other PCI access paths already enforced it.
* +2 Security-boundary bypass with practical sensitive-object access. Kernel lockdown is a meaningful security boundary intended to prevent even root from direct hardware access that can affect kernel integrity.
* +1 Integrity plausible. The commit explicitly connects PCI access lockdown to preventing userspace from programming DMA-capable hardware that could modify kernel code.

Paranoid additional signals:

* +2 Strong exploitation leverage. In the higher defensible interpretation, writable legacy I/O ports and mmap access to legacy PCI memory/I/O spaces can restore a class of hardware access that lockdown is meant to remove, including paths that may allow DMA-mediated tampering with kernel memory or code.

Non-awarded or limited signals:

* RealUAF not awarded. No lifetime, stale pointer, refcount, or memory-free primitive is present.
* Remote reachability not awarded. The vulnerable operations are local sysfs handlers, not packet-triggered paths.
* Namespace-scoped privilege not awarded. PCI sysfs access is host hardware management, not shown to be fully namespace-scoped.
* Confidentiality not separately awarded in the conservative score because the patch primarily establishes unauthorized access and kernel integrity risk, not a concrete readback disclosure chain.
* Availability not separately awarded because no independent crash path is required to establish the security boundary bypass.
* No host-admin penalty applied despite root being required, because the vulnerability is specifically a bypass of the lockdown boundary that is designed to restrict root-level users.

3. Reachability analysis

The direct trigger is local access to PCI legacy sysfs files, specifically `legacy_io` and `legacy_mem` style handlers. The commit states that root can still write arbitrary I/O ports and map legacy I/O and memory spaces while the kernel is locked down.

HostAdminRequired is YES because the supplied evidence positively identifies root-level access to these sysfs files as the demonstrated actor. However, this does not make the issue harmless, because kernel lockdown is a security mode that intentionally removes some kernel-tampering capabilities from root.

NamespaceScopedPrivilege is NO. The relevant resources are host PCI sysfs and host hardware access paths. The supplied evidence does not show an attacker-created namespace or container can complete the vulnerable operation.

No network trigger is established. Prior setup includes having kernel lockdown enabled and an affected architecture/path with PCI legacy handlers available. The patch mentions architectures defining `HAVE_PCI_LEGACY`, such as Alpha and PowerPC, but the supplied data is not enough to apply a strong rare-hardware penalty.

4. Primitive and severity interpretation

The exact primitive is an authorization/security-boundary bypass, not memory corruption. The missing `LOCKDOWN_PCI_ACCESS` check changes the intended decision from DENY under lockdown to ALLOW for legacy PCI I/O and memory handlers.

PrimitiveClass is CLASS_A because the patch directly restores a mandatory lockdown authorization check guarding direct hardware access. The demonstrated consequence is bypass of the lockdown policy. The higher-risk consequence is DMA or hardware-mediated modification of kernel memory or kernel code, which is technically connected to the purpose of the lockdown check and explicitly discussed in the commit context.

There is no UAF, no concrete repeated release/refcount operation, no controlled reclaim, and no arbitrary write primitive directly in kernel heap memory. Nevertheless, the security boundary is meaningful and the bypass may restore access to hardware mechanisms that lockdown exists to block.

ImportantCandidate is YES because lockdown bypasses are security-boundary issues and the patch context explicitly involves access capable of undermining kernel integrity. AutoDowngradeAllowed is NO because automatically treating this as ordinary root-only behavior would discard the lockdown security model.

Likely operational severity is high in systems that rely on Secure Boot or lockdown to prevent root from modifying kernel memory or kernel code. It is not remotely exploitable and is less relevant where lockdown is not used.

5. One-sentence report phrase

Missing lockdown checks in PCI legacy sysfs I/O and memory handlers allow root-level local access to bypass LOCKDOWN_PCI_ACCESS and regain direct hardware access that may undermine kernel integrity.

6. Manual review recommendation

MANUAL CHECK REQUIRED

This should be reviewed manually because it is a concrete lockdown security-boundary bypass, not a simple permission cleanup, and the commit explicitly ties the missing restriction to hardware access that may modify kernel code.

7. Call-site confidence

Call-site confidence: high

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

Patch: PCI/sysfs: Add lockdown checks to legacy I/O and memory handlers [ Upstream
Commit: cd07aef510ac6a2873e01f9ddddc5492490b0067
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cd07aef510ac6a2873e01f9ddddc5492490b0067

Changed files:
  drivers/pci/pci-sysfs.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=cd07aef510ac6a2873e01f9ddddc5492490b0067

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

The original Linux kernel CVE announcement for CVE-2026-90315 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90315

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:H/I:H/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: 5
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).