[CVE-2026-63878][MODERATE REGULAR] drm/amdgpu: check num_entries in GEM_OP GET_MAPPING_INFO

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

CVE: CVE-2026-63878
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu: check num_entries in GEM_OP GET_MAPPING_INFO
Commit: f059b4c493df3e54fe3ffe4658009c31864275da
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f059b4c493df3e54fe3ffe4658009c31864275da
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63878
Analysis date: Sun, 19 Jul 2026 12:05:55 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Low-like. Auto-close candidate
Manual review required: NO

Summary:
A local user with access to the amdgpu DRM device can pass an oversized `num_entries` value to `GEM_OP GET_MAPPING_INFO`, causing a kernel warning and potential panic on `panic_on_warn` systems, resulting in denial of service only.

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

The original Linux kernel CVE announcement for CVE-2026-63878 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63878

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 REGULAR
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-63878	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-789;*CWE-20;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A local denial of service can occur in the amdgpu GEM_OP GET_MAPPING_INFO ioctl because the user supplied num_entries value was used directly as the kvcalloc() element count. A very large num_entries can request an oversized allocation and trigger a kernel WARNING in __kvmalloc_node_noprof. On systems built or configured with panic_on_warn, this warning can become a kernel panic. For the CVSS the PR:L is used because triggering requires a local user or process with access to the amdgpu DRM device such as /dev/dri/renderD nodes, but full administrator privileges are not normally required on systems that expose GPU render nodes to users. The issue is not network reachable. Impact is denial of service only, with no supported evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like. Auto-close candidate (with actual score 3)  SKIP CVE-2026-63878 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	OOB SIMPLEFIX HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Low-like. Auto-close candidate**

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  The issue is reachable through the amdgpu DRM ioctl by a local process with access to `/dev/dri/renderD*` or equivalent GPU device nodes.

* Reliable kernel crash / strong DoS: +1
  The commit explicitly states that oversized `kvcalloc()` can trigger a kernel WARNING and panic on `CONFIG_PANIC_ON_WARN=y` systems.

Paranoid-only signal:

* Availability impact realistic: +1
  Counted only for the paranoid score because `panic_on_warn` can turn the warning into a host-wide crash. Without that configuration, the impact is closer to a warning/failed allocation path.

Not triggered:

* No generic memory corruption. The patch only adds an upper-bound validation check before allocation.
* No UAF, OOB write, double-free, type confusion, arbitrary write, or page-cache corruption.
* No privilege escalation plausibility.
* No confidentiality or integrity impact.
* No high-control GPU API bonus. This is object configuration via ioctl, but the patch does not show attacker control over object lifetime, reclaim, DMA mapping, pointer ownership, or overwrite targets.

## 3. Reachability analysis

A local user or process that can open the amdgpu DRM device can trigger the oversized allocation path by passing a very large `num_entries` value to `GEM_OP GET_MAPPING_INFO`. This does not require full root privileges on systems where render nodes are exposed to normal users, but it does require local device access. Containers or sandboxes only matter if the GPU device node is passed through. The path is not network reachable. The practical crash impact depends heavily on whether the kernel is configured to panic on warnings.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS issue, not an Important-class vulnerability. The theoretical impact is a host crash on `panic_on_warn` systems, but the patch does not support memory corruption, information disclosure, or privilege escalation. The conservative score remains low because the bug is an input-validation failure leading to an oversized allocation warning rather than a corruption primitive.

## 5. One-sentence report phrase

A local user with access to the amdgpu DRM device can pass an oversized `num_entries` value to `GEM_OP GET_MAPPING_INFO`, causing a kernel warning and potential panic on `panic_on_warn` systems, resulting in denial of service only.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as an auto-close candidate unless the affected product enables `panic_on_warn` broadly and exposes amdgpu render nodes to untrusted local users.

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

Patch: drm/amdgpu: check num_entries in GEM_OP GET_MAPPING_INFO
Commit: f059b4c493df3e54fe3ffe4658009c31864275da
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f059b4c493df3e54fe3ffe4658009c31864275da

Commit description:

kvcalloc(args->num_entries, sizeof(*vm_entries), GFP_KERNEL) at
amdgpu_gem.c:1050 uses the user-supplied num_entries directly without
any upper bounds check. Since num_entries is a __u32 and
sizeof(drm_amdgpu_gem_vm_entry) is 32 bytes, a large num_entries
produces an allocation exceeding INT_MAX, triggering
WARNING in __kvmalloc_node_noprof(), causing a kernel WARNING,
TAINT_WARN, and panic on CONFIG_PANIC_ON_WARN=y systems.

Add a size bounds check before we invoke the kvzalloc() to
reject oversized num_entries early with -EINVAL.

Fixes: 4d82724 ("drm/amdgpu: Add mapping info option for GEM_OP ioctl")
Signed-off-by: Ziyi Guo <n7l8m4@u.northwestern.edu>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 1fe7bf5 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/amdgpu_gem.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=f059b4c493df3e54fe3ffe4658009c31864275da

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

The original Linux kernel CVE announcement for CVE-2026-63878 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63878

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 3

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 REGULAR

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).