[CVE-2026-53051][LOW] PCI: tegra194: Fix CBB timeout caused by DBI access before core power-on [ Upstream

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

CVE: CVE-2026-53051
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: PCI: tegra194: Fix CBB timeout caused by DBI access before core power-on [ Upstream
Commit: 010983063a806720b45778d191335f8ea864fea3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=010983063a806720b45778d191335f8ea864fea3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53051
Analysis date: Fri, 26 Jun 2026 08:33:13 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
The Tegra194 PCIe endpoint driver may access DBI registers before the controller core is powered on during a repeated PERST deassert sequence, causing a CBB timeout and denial of service for the affected controller path.

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

The original Linux kernel CVE announcement for CVE-2026-53051 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53051

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53051	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';CWE-696;CWE-665;CWE-703;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.3';DESCR 'The Tegra194 PCIe endpoint driver can access DBI registers before the controller core is powered on when PERST is deasserted twice. This causes a CBB timeout because cleanup code can reach dw_pcie_dbi_ro_wr_en before reset_control_deassert has made the hardware operational. For the CVSS the PR:N is used because the relevant attacker model is an external PCIe host or reset controller that can drive the PERST sequence without credentials on the endpoint OS. The issue is not network reachable and is not triggered by normal packet traffic. Impact is denial of service for the affected PCIe endpoint controller or platform path, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1) 	MAYBE	INIT HARDWARE LINUS  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

* Firmware-mediated or external hardware influence: +1
  The trigger depends on PCIe PERST sequencing by an external host or reset controller, not on normal local userspace or network input.

* Reliable hardware DoS concern: +1 in paranoid scoring
  The described failure is a CBB timeout caused by DBI access before the Tegra194 PCIe controller core is powered on. This may disrupt the affected endpoint/controller path.

* Physical-only or rare hardware-specific condition: -2
  The issue is specific to Tegra194 PCIe endpoint mode and requires a particular PERST assert/deassert sequence. It is not a broadly reachable kernel interface.

* No memory corruption: +0
  The patch only reorders cleanup after `reset_control_deassert()`. There is no UAF, OOB write, object lifetime corruption, arbitrary write, or page-cache/shared-page corruption.

* No confidentiality or integrity impact: +0
  The failure mode is a hardware timeout/availability issue only.

## 3. Reachability analysis

The bug can be triggered by an external PCIe host or reset controller that can drive the PERST sequence twice. It is not reachable over the network and is not reachable through ordinary unprivileged local syscalls. Namespaces and containers do not materially lower the privilege requirement because the relevant control is hardware/reset sequencing, not a delegated kernel API. The affected path is device-specific and depends on Tegra194 PCIe endpoint deployment.

## 4. Severity interpretation

This behaves like a hardware-specific DoS or reliability bug, not an Important-class kernel vulnerability. The theoretical impact is limited to a CBB timeout or disruption of the PCIe endpoint/controller path. There is no evidence of memory corruption, privilege escalation, sensitive data exposure, or security-boundary bypass. The practical severity is Low-like or ordinary Moderate at most.

## 5. One-sentence report phrase

The Tegra194 PCIe endpoint driver may access DBI registers before the controller core is powered on during a repeated PERST deassert sequence, causing a CBB timeout and denial of service for the affected controller path.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is hardware-specific, availability-only, not network reachable, and not supported by any memory corruption or privilege-escalation primitive.

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

Patch: PCI: tegra194: Fix CBB timeout caused by DBI access before core power-on [ Upstream
Commit: 010983063a806720b45778d191335f8ea864fea3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=010983063a806720b45778d191335f8ea864fea3

Changed files:
  drivers/pci/controller/dwc/pcie-tegra194.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=010983063a806720b45778d191335f8ea864fea3

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

The original Linux kernel CVE announcement for CVE-2026-53051 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53051

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:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 4.3

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: 0
  Paranoid ActionableScore: 1

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