[CVE-2026-46309][IMPORTANT] drm/xe/uapi: Reject coh_none PAT index for CPU cached memory in madvise

[CVE-2026-46309][IMPORTANT] drm/xe/uapi: Reject coh_none PAT index for CPU cached memory in madvise

[AL-KERNEL]

CVE: CVE-2026-46309
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: drm/xe/uapi: Reject coh_none PAT index for CPU cached memory in madvise
Commit: 87f9b1528e1ffc1da3615d552c9a06aba5e20b00
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=87f9b1528e1ffc1da3615d552c9a06aba5e20b00
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46309
Analysis date: Mon, 08 Jun 2026 14:24:23 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local drm/xe information disclosure issue allows an iGPU user to select XE_COH_NONE for CPU cached memory, letting the GPU bypass CPU cache state and potentially read stale sensitive data from pages previously used by other processes.

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

The original Linux kernel CVE announcement for CVE-2026-46309 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46309

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-2026-46309	IMPORTANT	CHECK	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:N/A:N';*CWE-200;CWE-226;CWE-668;BEST CVSS score: '5.5';DESCR 'A local information disclosure issue in drm/xe madvise can occur when a user selects a PAT index with XE_COH_NONE for CPU cached memory on iGPU. With coh_none the GPU can bypass CPU caches and read directly from DRAM while the kernel page clear may still be dirty in CPU cache, so the GPU may observe stale sensitive data from pages previously used by other processes. For the CVSS the PR:L is used because a local process with access to the xe DRM ioctl or render node can trigger the configuration without full administrator privileges in typical desktop or compute deployments. The issue is not network reachable and does not require user interaction. Impact is confidentiality disclosure. No direct integrity or availability impact is supported by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	MAYBE	LEAK UAF DMAorINTERRUPT HARDWARE KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  The affected path is a DRM xe UAPI ioctl. On typical desktop or GPU compute systems, render nodes may be reachable by local non-root users.

* Security-boundary bypass with practical sensitive-object access: +2
  The bug can allow one process to observe stale data from pages previously used by other processes, bypassing normal memory isolation expectations.

* Confidentiality impact plausible: +1
  The commit explicitly describes leakage of stale sensitive data from freed pages.

* Broad/default/common subsystem or broadly deployed exposure: +1
  Intel iGPU systems with drm/xe and accessible render nodes are a realistic deployment class, even though the issue is limited to iGPU and newer affected kernels.

* Local unprivileged high-control kernel data-plane API: +1
  The DRM GPU VM and memory attribute UAPI lets users influence memory mappings and PAT coherency behavior at relatively fine granularity.

* Paranoid additional sensitive data exposure concern: +1
  In the worst case, stale physical memory may contain credentials, keys, service secrets, or other cross-process sensitive data. This does not imply code execution, but it raises triage priority.

No score was added for memory corruption, privilege escalation, remote reachability, or availability. The patch supports an information disclosure primitive, not UAF, OOB write, arbitrary write, or DoS.

## 3. Reachability analysis

A local process with access to the xe DRM ioctl or render node can trigger the vulnerable configuration by applying a XE_COH_NONE PAT index to CPU cached memory through madvise. This usually does not require full root privileges if the user is allowed to access the GPU render node. Containers may be affected if GPU devices are passed through or exposed to the container. The path is not network reachable. The issue is limited to iGPU because the described stale DRAM read condition depends on the non-coherent access behavior relevant to integrated GPU system memory.

## 4. Severity interpretation

This behaves more like an actionable Moderate or Strong Important candidate than an ordinary Moderate. There is no demonstrated memory corruption or privilege escalation path, so it should not be treated as a kernel code execution bug. However, the realistic impact is cross-process confidentiality loss through stale memory disclosure, which is a meaningful security boundary violation and should not be auto-closed based only on the moderate CVSS value.

## 5. One-sentence report phrase

A local drm/xe information disclosure issue allows an iGPU user to select XE_COH_NONE for CPU cached memory, letting the GPU bypass CPU cache state and potentially read stale sensitive data from pages previously used by other processes.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because this is a plausible cross-process information disclosure primitive through GPU memory coherency behavior, not a simple warning or DoS-only bug.

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

Patch: drm/xe/uapi: Reject coh_none PAT index for CPU cached memory in madvise
Commit: 87f9b1528e1ffc1da3615d552c9a06aba5e20b00
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=87f9b1528e1ffc1da3615d552c9a06aba5e20b00

Commit description:

Add validation in xe_vm_madvise_ioctl() to reject PAT indices with
XE_COH_NONE coherency mode when applied to CPU cached memory.

Using coh_none with CPU cached buffers is a security issue. When the
kernel clears pages before reallocation, the clear operation stays in
CPU cache (dirty). GPU with coh_none can bypass CPU caches and read
stale sensitive data directly from DRAM, potentially leaking data from
previously freed pages of other processes.

This aligns with the existing validation in vm_bind path
(xe_vm_bind_ioctl_validate_bo).

v2(Matthew brost)
- Add fixes
- Move one debug print to better place

v3(Matthew Auld)
- Should be drm/xe/uapi
- More Cc

v4(Shuicheng Lin)
- Fix kmem leak issues by the way

v5
- Remove kmem leak because it has been merged by another patch

v6
- Remove the fix which is not related to current fix

v7
- No change

v8
- Rebase

v9
- Limit the restrictions to iGPU

v10
- No change

Fixes: ada7486 ("drm/xe: Implement madvise ioctl for xe")
Cc: <stable@vger.kernel.org> # v6.18+
Cc: Shuicheng Lin <shuicheng.lin@intel.com>
Cc: Mathew Alwin <alwin.mathew@intel.com>
Cc: Michal Mrozek <michal.mrozek@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Jia Yao <jia.yao@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Acked-by: Michal Mrozek <michal.mrozek@intel.com>
Acked-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patch.msgid.link/20260417055917.2027459-2-jia.yao@intel.com
(cherry picked from commit 016ccdb )
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/xe/xe_vm_madvise.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=87f9b1528e1ffc1da3615d552c9a06aba5e20b00

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

The original Linux kernel CVE announcement for CVE-2026-46309 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46309

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
  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: 6
  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).