[CVE-2026-45878][IMPORTANT] drm/amdkfd: Fix watch_id bounds checking in debug address watch v2 [ Upstream

[CVE-2026-45878][IMPORTANT] drm/amdkfd: Fix watch_id bounds checking in debug address watch v2 [ Upstream

[AL-KERNEL]

CVE: CVE-2026-45878
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: drm/amdkfd: Fix watch_id bounds checking in debug address watch v2 [ Upstream
Commit: 971bf8e61e9b4abaacf9b35eaf76ec222758f9d6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=971bf8e61e9b4abaacf9b35eaf76ec222758f9d6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45878
Analysis date: Sat, 01 Aug 2026 11:54:35 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A userspace supplied large watch_id in the AMD KFD debug address watch path can bypass unsafe signed helper logic and reach an out of bounds write to pdd watch_points, causing kernel memory corruption and possible local DoS or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-45878 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45878

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-45878	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-129;CWE-681;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'A bounds checking flaw in the AMD KFD debug address watch path can allow a very large userspace supplied watch_id to pass through signed helper logic and trigger invalid bit shifts. If the ownership check is bypassed, the clear path can index pdd watch_points outside the fixed MAX_WATCH_ADDRESSES array and write outside the intended object. For the CVSS the PR:L is used because a local user or process with access to the amdkfd debug or GPU compute interface is needed, but full administrative privileges are not necessarily required in typical render group deployments. The issue is not network reachable and is triggered through a local device/control interface. Impact is at least a local denial of service via kernel memory corruption and in worst case may allow privilege escalation, so manual review is recommended.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)  SKIP CVE-2026-45878  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	OOB INIT HARDWARE TEST  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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

ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The input comes from userspace through the amdkfd debug address watch path, typically reachable by a local process with access to `/dev/kfd` or GPU compute/debug interfaces.
* Memory corruption, strong corruption primitive: +2. The patch and static-analysis warning explicitly identify an out-of-bounds access to `pdd->watch_points[watch_id]`, where the array has only `MAX_WATCH_ADDRESSES` entries.
* Weak LPE concern: +1. The primitive is an OOB write candidate in kernel memory, but the write value appears constrained because it is returned by `clear_address_watch()` rather than directly attacker-chosen.
* Reliable kernel crash / strong DoS: +1. Invalid shifts and out-of-bounds indexing can plausibly crash the kernel.
* Integrity impact plausible: +1. A kernel OOB write can corrupt adjacent kernel state, even if the exact target and payload are not demonstrated.
* No attacker-controlled payload or overwrite target certainty: -1. The offset is influenced by `watch_id`, but the actual write value and practical target control are not clearly demonstrated.

Paranoid additional interpretation:

* Strong LPE plausibility instead of weak LPE: +1 net increase. Because this is a local userspace-reachable OOB write in a kernel driver object, privilege escalation is technically defensible as a manual-review concern.
* Confidentiality impact plausible: +1. If adjacent kernel state can be corrupted or influenced, confidentiality impact cannot be ruled out at triage time, although no direct info leak is shown.

## 3. Reachability analysis

A local user or process that can access the AMD KFD debug or GPU compute interface can supply a large `watch_id`. Full host root is not necessarily required in systems where `/dev/kfd` is exposed to users in a GPU or render group. Containers or delegated GPU access may lower the practical privilege boundary if the device node is passed through.

The issue is not network reachable. It requires AMDGPU plus KFD support and the relevant debug address watch operation, so exposure is hardware and configuration dependent. However, it is still reachable through a normal local device/control interface on affected GPU systems.

Call-site confidence: high. The patch includes the vulnerable clear path and the exact OOB assignment to `pdd->watch_points[watch_id]`.

## 4. Severity interpretation

This should not be treated as an ordinary low-risk validation cleanup. The patch fixes signedness, invalid shift, and explicit bounds checking around a userspace-controlled index that can reach an array write in kernel memory.

Realistic exploitation evidence is incomplete because the payload and adjacent-object control are not demonstrated. Conservative handling is therefore Actionable Moderate. The paranoid score reaches Strong Important candidate because local kernel OOB writes in device drivers have historically been under-triaged and may become privilege-escalation primitives after manual analysis.

## 5. One-sentence report phrase

A userspace supplied large watch_id in the AMD KFD debug address watch path can bypass unsafe signed helper logic and reach an out of bounds write to pdd watch_points, causing kernel memory corruption and possible local DoS or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is userspace-reachable kernel memory corruption with an explicit OOB write candidate, even though the practical exploitability and payload control still need manual confirmation.

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

Patch: drm/amdkfd: Fix watch_id bounds checking in debug address watch v2 [ Upstream
Commit: 971bf8e61e9b4abaacf9b35eaf76ec222758f9d6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=971bf8e61e9b4abaacf9b35eaf76ec222758f9d6

Changed files:
  drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_debug.c:448
  drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_debug.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=971bf8e61e9b4abaacf9b35eaf76ec222758f9d6

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

The original Linux kernel CVE announcement for CVE-2026-45878 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45878

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:L/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 6
  Paranoid ActionableScore: 8

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).