[CVE-2026-63879][IMPORTANT] drm/amdgpu: fix amdgpu_hmm_range_get_pages

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

CVE: CVE-2026-63879
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: drm/amdgpu: fix amdgpu_hmm_range_get_pages
Commit: 2fd24407457a6b181ba827705678da70e528dcd0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2fd24407457a6b181ba827705678da70e528dcd0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63879
Analysis date: Sun, 19 Jul 2026 17:02:01 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An AMDGPU HMM notifier sequencing race can let the driver resolve or use invalidated pages during range walking, causing at least local DoS and requiring manual review for possible stale page confidentiality or integrity impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63879 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63879

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
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CVE-2026-63879	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	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-362;*CWE-416;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'amdgpu HMM range walking can use an inconsistent mmu interval notifier sequence if notifier_seq is read again during retry or chunked processing. This can let the driver work with invalid pages after a concurrent memory invalidation, creating a stale page reference or UAF style condition in GPU memory handling. For the CVSS the PR:L is used because triggering requires local code execution with access to the AMD GPU render or KFD interface, but not full administrative privileges in typical desktop or compute deployments. The issue is not network reachable and requires a race with user memory changes such as mapping invalidation while GPU HMM pages are being resolved. Impact is at least local denial of service and in the paranoid interpretation may include confidentiality or integrity impact if stale pages are later mapped or accessed by the GPU.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-63879 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX HARDWARE KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process with access to AMDGPU render or KFD interfaces can plausibly trigger HMM range handling without full host root privileges.
* Memory corruption, weak/indirect corruption candidate: +1. The patch says the driver could work with invalid pages, which indicates stale page or stale PFN handling, but does not show a controlled overwrite or reclaim primitive.
* Real lifetime corruption: +1. The bug is tied to MMU interval notifier sequencing and invalidated pages, which is a real page lifetime and invalidation consistency issue.
* Privileged kernel/device-management memory corruption path: +1. The affected path is GPU HMM page resolution, close to DMA and device memory mapping semantics.
* Availability impact realistic: +1. Working with invalid pages can plausibly cause GPU faults, driver failure, or kernel crash.
* Hard or unreliable race / special timing required: -1. Exploitation depends on a race with concurrent user memory invalidation while HMM pages are being resolved.

Paranoid additional signals:

* Weak LPE concern: +1. Stale page references in GPU memory handling can be security relevant if pages are later reused or mapped with wrong ownership, although no concrete reclaim primitive is shown.
* Confidentiality impact plausible: +1. A stale page mapping could theoretically expose memory belonging to a different object or process.
* Integrity impact plausible: +1. If the GPU later writes through a stale mapping, memory not intended for the attacker could be modified.

## 3. Reachability analysis

The bug is locally reachable through AMDGPU HMM related paths, likely requiring access to GPU render or KFD device nodes. This is usually not full administrative access, so PR:L is the practical CVSS-style interpretation. Namespaces and containers may matter if GPU device nodes are delegated into a container, because a container workload with device access could potentially reach the path. The issue is not network reachable. It is hardware and configuration dependent because an AMD GPU and HMM or KFD style memory interaction must be available, but this is not rare enough to auto-close because AMDGPU is a broadly deployed driver and the affected logic is in page lifetime handling.

Call-site confidence: medium. The provided patch contains the affected function and enough HMM notifier context to assess lifetime risk, but not all higher-level GPU ioctl or KFD call paths.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is not merely a warning, leak, or validation cleanup. The patch fixes an MMU notifier sequence lifetime issue that could leave the driver working with invalid pages. Realistically, the most likely impact is local DoS through GPU or kernel instability. Theoretical security impact is higher because stale page references in GPU mapping paths can become confidentiality or integrity issues, but the patch does not demonstrate attacker-controlled reclaim, arbitrary write, or reliable object replacement. Therefore the conservative score is Actionable Moderate, while the paranoid score is a Strong Important candidate requiring manual review.

## 5. One-sentence report phrase

An AMDGPU HMM notifier sequencing race can let the driver resolve or use invalidated pages during range walking, causing at least local DoS and requiring manual review for possible stale page confidentiality or integrity impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: this is a race in GPU HMM page lifetime handling with possible stale page or UAF-style consequences, and the difference between DoS-only and possible C/I impact depends on call-path and page reuse behavior not fully shown in the patch.

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UPSTREAM PATCH SUMMARY
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Patch: drm/amdgpu: fix amdgpu_hmm_range_get_pages
Commit: 2fd24407457a6b181ba827705678da70e528dcd0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2fd24407457a6b181ba827705678da70e528dcd0

Commit description:

The notifier sequence must only be read once or otherwise we could work
with invalid pages.

While at it also fix the coding style, e.g. drop the pre-initialized
return value and use the common define for 2G range.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Tested-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit c08972f )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.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=2fd24407457a6b181ba827705678da70e528dcd0

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

The original Linux kernel CVE announcement for CVE-2026-63879 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63879

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:L/UI:N/S:U/C:L/I:L/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).