Bug 2541330 (CVE-2026-98106)

Summary:	CVE-2026-98106 kernel: drm/pagemap: Prevent double migration of device pages
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's Direct Rendering Manager (DRM) pagemap component. A race condition during memory migration allows a local user to cause a Denial of Service (DoS). When device-private memory is migrated to system memory during a page fault, a timing window permits an eviction process to concurrently attempt migrating the same memory folio again. This double migration leaves internal memory tracking lists in an inconsistent state, causing the kernel to retry locks indefinitely and resulting in a system lockup.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-25 11:26:13 UTC

In the Linux kernel, the following vulnerability has been resolved:

drm/pagemap: Prevent double migration of device pages

A device-private folio migrated to system memory by a CPU fault can
remain reachable through the raw-PFN eviction path until migration
finalization drops the source reference.

If eviction selects the same device-private folio during this window,
it can attempt to migrate the folio again. The second migration can leave
an uncharged folio on an LRU list, causing folio_lruvec_lock_irqsave() to
retry indefinitely and resulting in a soft lockup and RCU stall.

Mark successfully migrated device-private folios using a low bit of
their zone_device_data before migration finalization. Make both CPU-fault
and raw-PFN migration paths skip device-private folios carrying this
flag.

Mask the flag when retrieving the drm_pagemap_zdd pointer and preserve
it when a device-private folio is split. Keeping the state on the physical
folio also avoids depending on a virtual address that may change before a
fault occurs.

v2:
- Replace the retired-PFN XArray with an embedded bitmap. (Matthew Brost)
- Mark every base page covered by a migrated folio so retirement remains
  valid if the folio is later split.

v3:
- Store the migrated state in a low bit of zone_device_data instead of
  adding virtual-range and bitmap tracking to the ZDD. (Matthew Brost)
- Mask the flag when retrieving the ZDD and preserve it when splitting
  a folio.
- Drop the pre-existing fixes already covered by Matthew Brost's series:
  https://patchwork.freedesktop.org/series/171651/

v4:
- Advance by the folio size only for migration entries marked with
  MIGRATE_PFN_COMPOUND. (Sashiko)

v5:
- Simplify ZDD flag updates and folio iteration. (Matthew Brost)
- Skip retired device-private folios in the CPU-fault path. (Matthew Brost)
- Preserve flag bits while taking a new ZDD reference for split folios.

v6:
- Restore MIGRATE_PFN_COMPOUND-aware stepping so non-compound migration
  entries are processed one at a time. (Sashiko)
- Drop the pre-existing fixes already covered by Matthew Brost's series:
  https://patchwork.freedesktop.org/series/171651/

The lockup was observed as:
[10109.860465] watchdog: BUG: soft lockup - CPU#9 stuck for 26s! [kworker/u65:5:6557]
[10109.860524] Tainted: [S]=CPU_OUT_OF_SPEC, [O]=OOT_MODULE
[10109.860524] Hardware name: ASUS System Product Name/PRIME Z790-P WIFI, BIOS 0812 02/24/2023
[10109.860525] Workqueue: xe_page_fault_work_queue xe_pagefault_queue_work [xe]
[10109.860644] RIP: 0010:_raw_spin_unlock_irqrestore+0x57/0x80
[10109.860655] Call Trace:
[10109.860655]  <TASK>
[10109.860657]  folio_lruvec_lock_irqsave+0x216/0x220
[10109.860661]  ? __pfx_lru_add+0x10/0x10
[10109.860665]  folio_batch_move_lru+0xc8/0x450
[10109.860670]  ? lock_acquire+0xc4/0x2d0
[10109.860674]  ? __folio_batch_add_and_move+0x60/0x2e0
[10109.860677]  ? folio_migrate_mapping+0xa6/0x110
[10109.860679]  ? folio_migrate_flags+0x13b/0x1b0
[10109.860681]  ? __pfx_lru_add+0x10/0x10
[10109.860683]  __folio_batch_add_and_move+0xe7/0x2e0
[10109.860685]  ? dma_iova_try_alloc+0xb0/0x140
[10109.860689]  folio_add_lru+0x64/0x80
[10109.860691]  __migrate_device_finalize+0x12c/0x270
[10109.860695]  migrate_device_finalize+0x10/0x20
[10109.860698]  drm_pagemap_evict_to_ram+0x185/0x370 [drm_gpusvm_helper]
[10109.860704]  ? drm_pagemap_evict_to_ram+0x96/0x370 [drm_gpusvm_helper]
[10109.860709]  xe_svm_bo_evict+0x15/0x20 [xe]
[10109.860819]  ? xe_svm_bo_evict+0x15/0x20 [xe]
[10109.860921]  xe_bo_move+0x107e/0x1570 [xe]
[10109.860992]  ? xe_ttm_tt_create+0x168/0x340 [xe]
[10109.861059]  ? __up_read+0x98/0x2b0
[10109.861061]  ? lock_is_held_type+0xa3/0x130
[10109.861067]  ttm_bo_handle_move_mem+0xe8/0x1e0 [ttm]
[10109.861075]  ttm_bo_evict+0x141/0x1c0 [ttm]
[10109.861081]  ttm_bo_evict_cb+0x9f/0x100 [ttm]
[10109.861086]  ttm_lru_walk_for_evict+0x84/0x190 [ttm]
[10109.861091]  ? xe_ttm_vram_mgr_new+0x258/0x3a0 [xe]
[10109.861198]  ttm_bo_alloc_resource+0x219/0
---truncated---

Comment 1 Keith Grant 2026-09-28 11:56:34 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98106.mbox