[CVE-2026-64460][MODERATE 7.0] PCI/IOV: Skip VF Resizable BAR restore on read error

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-64460
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: PCI/IOV: Skip VF Resizable BAR restore on read error
Commit: b77524621250407386f44c6eea7e5e4619ada1ce
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b77524621250407386f44c6eea7e5e4619ada1ce
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64460
Analysis date: Sat, 25 Jul 2026 14:30:34 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A failed PCI VF Resizable BAR config read can decode PCI_ERROR_RESPONSE as nbars 7 and bar_idx 7, causing an out-of-bounds kernel read during SR-IOV BAR restore and potentially a local hardware-dependent DoS.

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

The original Linux kernel CVE announcement for CVE-2026-64460 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64460

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-2026-64460	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-129;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.8';DESCR 'PCI/IOV VF Resizable BAR restore can read PCI_ERROR_RESPONSE from an unreachable device and decode it as nbars 7 and bar_idx 7. This makes sriov_restore_vf_rebar_state access dev sriov barsz outside its 6 element array and triggers an out of bounds kernel read. The realistic impact is a local hardware dependent denial of service or UBSAN splat during PCI state restore, especially if warning conditions are fatal. For the CVSS the PR:L is used for the paranoid score because delegated PCI or GPU management can exist for local service accounts or containerized workloads without full host root. The issue is not network reachable. Impact is at least availability loss and in the paranoid interpretation may allow limited confidentiality or integrity impact due to an out of bounds kernel read and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	WRITE KASAN OOB HARDWARE LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* +1 Firmware-mediated external influence. The trigger depends on a PCI device becoming unreachable and returning PCI_ERROR_RESPONSE during config reads.
* +1 Memory corruption, weak or indirect candidate. The failed config read is decoded into nbars 7 and bar_idx 7, causing an out-of-bounds read from a 6 element kernel array.
* +1 Privileged kernel/device-management memory corruption path. The bug is in PCI SR-IOV VF Resizable BAR restore during pci_restore_state().
* +1 Availability impact realistic. UBSAN reports an array-index-out-of-bounds splat and systems with fatal warnings may see DoS.
* -2 Requires admin or device-management privileges in typical deployments. Reliable triggering usually requires reset, restore, suspend/resume, GPU power-state recovery, or similar privileged device-management conditions.

Paranoid additions/interpretation:

* +1 Local lower-privilege delegated trigger concern. Some environments delegate GPU or PCI device management to service accounts, containers, or VM stacks without full host-root equivalence.
* +1 Reliable kernel crash / strong DoS in hardened builds. UBSAN or panic_on_warn configurations can turn this into a stronger availability event.
* -1 Corruption primitive highly constrained. The primitive is an OOB read of one array element used for BAR size restoration, not an attacker-controlled overwrite or UAF reclaim primitive.

## 3. Reachability analysis

The realistic trigger is local and hardware-dependent. It requires a PCI SR-IOV capable device with VF Resizable BAR state, followed by a restore path while config reads return 0xffffffff. This was observed on an NVIDIA GPU after a failed GC6 power-state exit.

Typical exploitation requires privileged control over PCI device reset, power management, suspend/resume, driver recovery, or GPU management. Namespace or container environments may lower the practical privilege barrier if device management is delegated, but this is not a normal unprivileged syscall path. The issue is not network reachable.

Call-site confidence: high, because the patch shows the exact read, decode, array index, and subsequent restore path.

## 4. Severity interpretation

This is not an Important-class candidate by default. The demonstrated primitive is an out-of-bounds kernel read from dev->sriov->barsz[] caused by trusting PCI_ERROR_RESPONSE as a valid control register value. There is no supported evidence of UAF, OOB write, arbitrary write, object replacement, callback control, or direct privilege escalation.

Realistically this behaves like a device-specific local DoS or warning/panic condition in PCI restore. Paranoid handling reaches Actionable Moderate because it is a kernel memory-safety issue in a privileged PCI/device-management path, and delegated GPU or device-management deployments may reduce practical privilege requirements.

## 5. One-sentence report phrase

A failed PCI VF Resizable BAR config read can decode PCI_ERROR_RESPONSE as nbars 7 and bar_idx 7, causing an out-of-bounds kernel read during SR-IOV BAR restore and potentially a local hardware-dependent DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real kernel out-of-bounds read in PCI restore state, but exploitation appears local, constrained, and hardware-dependent, so it should be reviewed manually rather than auto-closed or escalated directly to Important.

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

Patch: PCI/IOV: Skip VF Resizable BAR restore on read error
Commit: b77524621250407386f44c6eea7e5e4619ada1ce
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b77524621250407386f44c6eea7e5e4619ada1ce

Commit description:

sriov_restore_vf_rebar_state() uses the VF Resizable BAR Control register
to decide how many VF BARs to restore (nbars) and which VF BAR each
iteration addresses (bar_idx). bar_idx indexes into dev->sriov->barsz[],
which has only PCI_SRIOV_NUM_BARS (6) entries.

When a device does not respond, config reads typically return
PCI_ERROR_RESPONSE (~0).  Both fields are 3 bits wide, so nbars and bar_idx
both evaluate to 7. The barsz[] access then goes out of bounds.  UBSAN
reports this as:

  UBSAN: array-index-out-of-bounds in drivers/pci/iov.c:948:51 index 7 is out of range for type 'resource_size_t [6]'

Observed on an NVIDIA RTX PRO 1000 GPU (GB207GLM) that stopped responding
during a failed GC6 power state exit. The subsequent pci_restore_state()
invoked sriov_restore_vf_rebar_state() while config reads returned
0xffffffff, triggering the splat.

Bail out if any VF Resizable BAR Control read returns PCI_ERROR_RESPONSE.
No further VF BARs are touched, which is safe because a config read that
returns PCI_ERROR_RESPONSE indicates the device is unreachable and
restoration is pointless. This mirrors the guard in
pci_restore_rebar_state().

Fixes: 5a8f77e ("PCI/IOV: Restore VF resizable BAR state after reset")
Signed-off-by: Marco Nenciarini <mnencia@kcore.it>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/44a4ae53ec2825816b816c85cd378430d9a95cc6.1776429882.git.mnencia@kcore.it
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/pci/iov.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=b77524621250407386f44c6eea7e5e4619ada1ce

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

The original Linux kernel CVE announcement for CVE-2026-64460 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64460

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:N/A:L
  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: 2
  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: NO
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).