[CVE-2026-68436][LOW] drm/amd/display: use kvzalloc to allocate struct dc

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

CVE: CVE-2026-68436
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amd/display: use kvzalloc to allocate struct dc
Commit: dbad70d40cad9c5e7586953275287fe7531fb811
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dbad70d40cad9c5e7586953275287fe7531fb811
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68436
Analysis date: Tue, 11 Aug 2026 20:53:47 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-68436 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68436

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.

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

CVE-2026-68436	LOW	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:H/UI:N/S:U/C:N/I:N/A:H';CWE-789;**CWE-400;CWE-770;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'AMD Display Core allocated the large struct dc object with kzalloc, which requires physically contiguous memory. On some builds the object can cross the page allocator order limit, causing allocation failure during dc_create and making amdgpu display initialization abort. For the CVSS the PR:H is used because reliable triggering normally requires administrative control over driver loading, kernel build or device probe behavior. The issue is not network reachable and is tied to local hardware initialization rather than remote input. Impact is denial of service for display availability, 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)  SKIP CVE-2026-68436 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	WARNONLY DMAorINTERRUPT HARDWARE 	-	-	checked

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

ActionableScore=1

1. ActionableScore
* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Availability impact realistic: +1. `amdgpu` display initialization can fail, leaving the display unusable.
* Broad deployed driver family: +1 in paranoid interpretation only. AMDGPU is common, but the affected condition is build/config/compiler-size dependent.
* Requires admin/root/CAP_* or equivalent for reliable triggering: -2. Practical control normally requires changing kernel build/config, compiler behavior, driver load/probe conditions, or device initialization.
* Rare/config-dependent condition: -1. The issue depends on `struct dc` exceeding the contiguous allocation threshold in a specific build and hardware path.
* No memory corruption signal. The patch changes allocation API from `kzalloc` to `kvzalloc` and matching free API from `kfree` to `kvfree`.
* No LPE, confidentiality, integrity, UAF, OOB, double-free, or page-cache/shared-page primitive is supported.

3. Reachability analysis
The bug is reached during AMDGPU Display Core initialization in `dc_create()`. It is not network reachable and is not a normal unprivileged local trigger. Affected systems can fail automatically at boot or device probe if the built `struct dc` size crosses the page allocator contiguous allocation limit. Namespaces and containers do not materially lower the privilege requirement because triggering depends on host driver initialization, kernel build properties, and AMD GPU hardware presence. Call-site confidence: high, because the commit message gives the failing call path and the patch directly changes the allocation and free sites.

4. Severity interpretation
This behaves like a Low-like or ordinary Moderate availability issue, not an Important-class vulnerability. The realistic impact is failed GPU display initialization and unusable display output. There is no demonstrated memory corruption or security boundary bypass. The theoretical worst case is stronger availability impact on systems where the affected AMDGPU display path is required for operation, but the patch context does not support privilege escalation, data corruption, or information disclosure.

5. One-sentence report phrase
AMD Display Core used `kzalloc()` for a very large software-only `struct dc`, which can exceed contiguous page allocation limits in some builds and cause AMDGPU display initialization to fail, resulting in local availability impact only.

6. Manual review recommendation
NO MANUAL CHECK NEEDED.
This can be handled as an allocation-failure availability bug with no concrete exploitation primitive, no unprivileged trigger, and no evidence of memory corruption or privilege escalation.

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

Patch: drm/amd/display: use kvzalloc to allocate struct dc
Commit: dbad70d40cad9c5e7586953275287fe7531fb811
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dbad70d40cad9c5e7586953275287fe7531fb811

Commit description:

struct dc has grown large over time (most of it the two inlined
dc_scratch_space copies) and now sits close to the page allocator's 4 MiB
contiguous allocation limit. Its actual size is not fixed by the source
alone, it also depends on the compiler and the .config, so it can easily
cross 4 MiB, e.g. with a newer GCC or a config change.

dc_create() allocates it with kzalloc(). Once struct dc exceeds 4 MiB the
request is rounded up to order 11 (8 MiB), which is above MAX_PAGE_ORDER,
so the page allocator warns and returns NULL. dc_create() then fails, DM
init fails and amdgpu probe aborts with -EINVAL:

  WARNING: mm/page_alloc.c:5197 at __alloc_frozen_pages_noprof+0x2f9/0x380
   dc_create+0x38/0x660 [amdgpu]
   amdgpu_dm_init+0x2d9/0x510 [amdgpu]
   dm_hw_init+0x1b/0x90 [amdgpu]
   amdgpu_device_init.cold+0x150d/0x1e13 [amdgpu]
   amdgpu_driver_load_kms+0x19/0x80 [amdgpu]
   amdgpu_pci_probe+0x1e2/0x4c0 [amdgpu]

dc_create() then returns NULL and DM init fails, which aborts the whole
GPU init and makes amdgpu probe fail with -EINVAL ("hw_init of IP block
<dm> failed -22"), leaving the display unusable. The subsequent
amdgpu_irq_put() warnings during teardown are just fallout of unwinding
a half-initialized device.

struct dc is a software-only bookkeeping structure that is never handed
to hardware DMA and is only ever kept as an opaque pointer, so it does
not require physically contiguous memory. Allocate it with kvzalloc()
(and free it with kvfree()) so that the allocator can fall back to
vmalloc() when a contiguous allocation of that size is not available,
which also avoids the MAX_PAGE_ORDER warning entirely.

v2:
 - Rebase to amd-staging-drm-next.

Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/5406
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Honglei Huang <honghuan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 991e051 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  mm/page_alloc.c
  drivers/gpu/drm/amd/display/dc/core/dc.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=dbad70d40cad9c5e7586953275287fe7531fb811

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

The original Linux kernel CVE announcement for CVE-2026-68436 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68436

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:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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: unknown
  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).