* [CVE-2026-89815][MODERATE 7.0] drm/ttm: Drop tt->restore after successful restore
@ 2026-09-16 15:20 AL-KERNEL
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From: AL-KERNEL @ 2026-09-16 15:20 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-89815
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: drm/ttm: Drop tt->restore after successful restore
Commit: a46ab76b6cf5478e2ac7b942a377c7a1827b436a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a46ab76b6cf5478e2ac7b942a377c7a1827b436a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89815
Analysis date: Wed, 16 Sep 2026 11:20:31 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89815 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89815
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 7.0
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-2026-89815 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89815 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';*CWE-664;CWE-459;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A stale restore state in the DRM TTM pool restore path can remain after ttm_pool_restore_and_alloc completes successfully. Later backup restore flows may treat the TTM object as already restored while shmem handles are still present in tt pages, which can lead to invalid page handling and a crash in sg_alloc_append_table_from_pages during Xe GPU memory validation. For the CVSS the PR:L is used because triggering the affected path requires local DRM ioctl access, which may be available to an unprivileged user with access to the GPU render node. The issue is not network reachable and is triggered through local GPU memory management operations. Impact is at least local denial of service via kernel crash. In the paranoid interpretation, limited confidentiality or integrity impact is kept possible because stale memory manager state can lead to invalid pointer use, but there is no strong evidence for a reliable privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate (with actual score 5) YES DANGER HARDWARE KPANIC YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate**::
No floor or cap changed the score.
2. Signal breakdown
Conservative positive signals:
* +1 weak or indirect corruption candidate: `tt->pages` can retain shmem handles where later code expects page objects, leading to invalid structured interpretation in `sg_alloc_append_table_from_pages`.
* +1 reliable kernel crash or strong DoS: supplied trace shows crash path through `sg_alloc_append_table_from_pages`, `xe_tt_map_sg`, `xe_bo_move`, and `xe_exec_ioctl`.
* +1 local below-host-admin reachability: the visible path is a DRM Xe ioctl path, normally reachable by a local process with GPU render access rather than host administrator privileges.
* +1 device or GPU memory-management state corruption concern: the invalid state affects TTM page restoration and SG/DMA mapping preparation, not just passive metadata.
Paranoid additional signal:
* +1 weak LPE or stronger-impact concern: the wrong semantic content in `tt->pages` is later consumed by GPU memory validation and SG construction. This is not proof of privilege escalation, but it is enough to keep a limited unresolved C/I concern for manual review.
Negative or non-awarded signals:
* Real UAF not awarded: the patch shows stale restore state and wrong page-array contents, but not a freed object later dereferenced.
* Concrete repeated release/refcount not awarded: there is no visible first release that can end lifetime followed by a second put/free/refcount mutation on the exact same dangling reference.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Callback or function-pointer control not demonstrated.
* Remote reachability not established.
* Extra availability point not awarded because the same crash is already counted once.
* Strong LPE leverage +2 not awarded because the patch does not establish controlled replacement, directed corruption, or credential/security-object overwrite.
* CLASS_A not used because the primitive is invalid active memory-manager state, not a demonstrated strong corruption primitive.
Repeated release/refcount checklist:
* First release can end lifetime: not established.
* Exact same reference survives into second lifetime mutation: not established.
* Second operation is a real lifetime/refcount mutation: not established.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 from repeated release/refcount applied: no.
3. Reachability analysis
The visible trigger path is local and goes through DRM/Xe GPU ioctl execution and validation: `xe_exec_ioctl`, `xe_validation_exec_lock`, `drm_gpuvm_validate`, `xe_gpuvm_validate`, `xe_bo_validate`, and `xe_tt_map_sg`.
The likely attacker is a local process with access to the relevant DRM render node or graphics device. This is below host-admin in common deployments where render-node access is delegated to users or services, so `HostAdminRequired=NO`. This is not namespace-scoped, so `NamespaceScopedPrivilege=NO`.
There is no network trigger. Prior setup requires a system using the Xe driver and TTM backup/restore path, but common workstation/server GPU hardware is not treated as rare hardware by itself. The bug is not described as a timing race. It is an ordered state-management problem after a successful restore.
For DRM role separation:
* ordinary logged-in user: possible if granted render-node access;
* DRM master or compositor: possible actor depending on deployment;
* delegated graphics service: possible actor;
* host administrator: not required by the visible ioctl path;
* remote attacker: not supported.
4. Primitive and severity interpretation
The exact primitive is stale restore-state handling in `ttm_pool_restore_and_alloc`. After `ttm_pool_restore_commit` succeeds, `tt->restore` was not freed and cleared. Later backup/restore flows could treat the TTM object as restored while shmem handles remained in `tt->pages`. Those entries are then consumed as page-related data during SG table construction, causing invalid page handling and a kernel crash.
This is an active structured state bug in GPU memory management, not fixed stale storage and not a proven UAF. It is also not just passive bookkeeping because the stale state is later consumed by active memory validation and SG construction.
Primitive class is CLASS_B because the bug creates a meaningful active kernel memory-management consistency violation with invalid structured interpretation. It is not CLASS_A because controlled reclaim, arbitrary R/W, callback control, or demonstrated LPE are not established.
Demonstrated consequence: local kernel crash / DoS.
Speculative consequence: limited C/I impact may be possible if invalid `tt->pages` contents can be shaped or consumed in a more useful way, but this is not proven by the supplied patch.
ImportantCandidate=NO because the current evidence does not establish strong exploitation leverage beyond crash. ManualReview=RECOMMENDED because the issue is reachable through a local DRM ioctl path and affects GPU memory-manager state rather than a simple isolated warning. AutoDowngradeAllowed=NO because automatically closing it as ordinary low-risk DoS could miss unresolved memory-manager exploitation implications.
Likely operational severity: actionable Moderate.
5. One-sentence report phrase
A stale restore state in the DRM TTM restore path can leave shmem handles in `tt->pages`, causing later Xe GPU memory validation to interpret invalid entries as pages and crash the kernel through local DRM ioctl activity.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: local DRM render access may be below host-admin, and the bug affects active GPU memory-management state with invalid structured interpretation, although no real UAF, arbitrary write, or proven privilege-escalation primitive is established.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: drm/ttm: Drop tt->restore after successful restore
Commit: a46ab76b6cf5478e2ac7b942a377c7a1827b436a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a46ab76b6cf5478e2ac7b942a377c7a1827b436a
Commit description:
ttm_pool_restore_and_alloc() can successfully complete the restore
process via ttm_pool_restore_commit(), but tt->restore is not dropped
afterward. As a result, subsequent backup/restore flows observe what
appears to be a completed restore, while in reality shmem handles are
still installed in tt->pages, leading to the stack trace below.
Fix this by freeing and dropping tt->restore in
ttm_pool_restore_and_alloc() upon successful completion of the restore.
20545 [ 309.784531] RIP: 0010:sg_alloc_append_table_from_pages+0x38c/0x490
20547 [ 309.809570] RSP: 0018:ffffc9000623b838 EFLAGS: 00010206
20548 [ 309.814827] RAX: 0000000000001000 RBX: ffff88816e42a160 RCX: 0000000000000000
20549 [ 309.821986] RDX: 0000000000002000 RSI: 0000000000000003 RDI: 0000000000001000
20550 [ 309.829147] RBP: ffff88816e42a168 R08: 0000000000000002 R09: 000000007ffff000
20551 [ 309.836310] R10: ffffc9000623b928 R11: 0000000000000000 R12: 000000007ffff000
20552 [ 309.843471] R13: ffff88815ba5a100 R14: 0000000000000000 R15: 0000000000000001
20553 [ 309.850634] FS: 00007f9ff305e700(0000) GS:ffff888276c94000(0000) knlGS:0000000000000000
20554 [ 309.858749] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
20555 [ 309.864519] CR2: 00007f9fca701000 CR3: 00000001565e2005 CR4: 0000000008f70ef0
20556 [ 309.871678] PKRU: 55555558
20557 [ 309.874403] Call Trace:
20558 [ 309.876866] <TASK>
20559 [ 309.878988] sg_alloc_table_from_pages_segment+0x60/0x100
20560 [ 309.884415] ? ttm_resource_manager_usage+0x36/0x60 [ttm]
20561 [ 309.889845] ? xe_tt_map_sg+0x7d/0xd0 [xe]
20562 [ 309.894045] xe_tt_map_sg+0x7d/0xd0 [xe]
20563 [ 309.898037] xe_bo_move+0x927/0xaa0 [xe]
20564 [ 309.902029] ttm_bo_handle_move_mem+0xba/0x170 [ttm]
20565 [ 309.907022] ttm_bo_validate+0xbe/0x190 [ttm]
20566 [ 309.911405] xe_bo_validate+0x9a/0x120 [xe]
20567 [ 309.915663] xe_gpuvm_validate+0xd9/0x140 [xe]
20568 [ 309.920206] drm_gpuvm_validate+0x2f0/0x5b0 [drm_gpuvm]
20569 [ 309.925459] ? drm_exec_lock_obj+0x63/0x210 [drm_exec]
20570 [ 309.930627] xe_vm_validate_rebind+0x46/0xb0 [xe]
20571 [ 309.935428] xe_exec_fn+0x20/0x40 [xe]
20572 [ 309.939249] drm_gpuvm_exec_lock+0x78/0xc0 [drm_gpuvm]
20573 [ 309.944410] xe_validation_exec_lock+0x5a/0xa0 [xe]
20574 [ 309.949385] xe_exec_ioctl+0x806/0xc30 [xe]
20575 [ 309.953639] ? ttwu_queue_wakelist+0xd9/0xf0
20576 [ 309.957935] ? __pfx_xe_exec_fn+0x10/0x10 [xe]
20577 [ 309.962449] ? __wake_up_common+0x73/0xa0
20578 [ 309.966482] ? __pfx_xe_exec_ioctl+0x10/0x10 [xe]
20579 [ 309.971263] drm_ioctl_kernel+0xa3/0x100
20580 [ 309.975209] drm_ioctl+0x213/0x440
20581 [ 309.978637] ? __pfx_xe_exec_ioctl+0x10/0x10 [xe]
20582 [ 309.983415] xe_drm_ioctl+0x67/0xd0 [xe]
20583 [ 309.987408] __x64_sys_ioctl+0x7f/0xd0
Cc: Thomas Hellström <[email protected]>
Cc: Christian Koenig <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: Matthew Auld <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Simona Vetter <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Fixes: b63d715 ("drm/ttm/pool, drm/ttm/tt: Provide a helper to shrink pages")
Signed-off-by: Matthew Brost <[email protected]>
Reviewed-by: Thomas Hellström <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/gpu/drm/ttm/ttm_pool.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=a46ab76b6cf5478e2ac7b942a377c7a1827b436a
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-89815 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89815
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:N/I:N/A:H
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 5.8
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: 4
Paranoid ActionableScore: 5
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: YES
Published priority for this report (same as in Subject): MODERATE 7.0
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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