CVE-2026-68384 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/xe/vf: Fix VF CCS attach/detach race with in-flight BO moves
xe_bo_move() attaches VF CCS read/write batch buffers (BBs) to a BO after it transitions NULL/SYSTEM -> TT, and detaches them after it transitions TT -> SYSTEM. Both operations were done synchronously on the CPU immediately after building the move's copy/clear fence, without waiting for that fence to signal. This creates two races with VF migration:
- Attach happens too late relative to the copy job it is meant to protect. If the copy job is submitted before the CCS BBs are attached, a VF migration event that pauses execution mid-copy can observe partially copied CCS metadata without the attach state needed to correctly save/restore it.
- Detach happens too early relative to the copy job that moves data out of TT. The CCS BBs are torn down right after the copy fence is obtained, while the actual blit may still be in flight. A VF migration event that pauses execution mid-copy can then race the save/restore path against the still-running blit, and the CCS BBs it would need to make sense of the paused state have already been removed.
Fix both races:
- Move the attach call to before the copy/clear job is submitted, so the CCS BBs are already registered by the time the copy runs. On attach failure, unwind and bail out of the move. xe_migrate_ccs_rw_copy() now takes the destination resource explicitly, since bo->ttm.resource is not updated to the new resource until after the move commits.
- Detach only after explicitly waiting for the copy fence to signal, instead of tearing down the CCS BBs immediately after obtaining it.
While here, also fix xe_sriov_vf_ccs_attach_bo() to properly unwind and propagate errors: the per-context loop previously never broke out on error, silently discarding earlier failures. Unwind by clearing each attached context directly via xe_migrate_ccs_rw_copy_clear() instead of reusing xe_sriov_vf_ccs_detach_bo(), which requires both contexts to be attached before it will clean up either one.
(cherry picked from commit d45ad0aa7a1eb5d7288b5ed948b05695611dc39e)
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Analysis
by VulDB Data Team • 08/10/2026
This vulnerability exists within the Linux kernel's graphics subsystem, specifically affecting the xeon edgerton (xe) driver's virtual function (VF) implementation for graphics processing units. The issue stems from a race condition in how read/write batch buffers are managed during buffer object (BO) migration operations, particularly when transitioning between different memory types such as NULL/SYSTEM and TT (translation table). The vulnerability directly impacts the integrity of graphics memory management and could potentially lead to data corruption or system instability during concurrent graphics operations.
The technical flaw manifests in two distinct race conditions that occur during the xe_bo_move() function execution. First, the attachment of VF CCS (Cache Coherency State) read/write batch buffers happens too late in the process, after the copy job has already been submitted but before it completes. This timing issue creates a scenario where a VF migration event can observe partially copied CCS metadata without the proper attach state needed for correct save/restore operations. Second, the detachment of these same CCS BBs occurs too early, immediately after obtaining the copy fence rather than waiting for the actual blit operation to complete. This premature cleanup allows VF migration events to race against still-running blit operations, where the necessary CCS BBs for understanding the paused state have already been removed.
The operational impact of this vulnerability extends beyond simple memory management issues and could potentially enable privilege escalation or denial of service conditions within graphics-intensive applications. According to CWE classification, this represents a race condition vulnerability (CWE-362) that occurs during concurrent access to shared resources. The ATT&CK framework would categorize this under privilege escalation techniques through kernel vulnerabilities, as improper synchronization can allow attackers to manipulate memory state in ways that bypass normal access controls. The fix implemented addresses both races by reordering operations and adding proper synchronization points, moving the attach call before job submission and ensuring detach only occurs after explicit fence signaling.
The resolution involves several key modifications to the graphics driver's migration logic. The xe_migrate_ccs_rw_copy() function now requires explicit destination resource parameters since the BO's TTM resource is not updated until after the move commits, preventing potential timing issues with resource access. The error handling in xe_sriov_vf_ccs_attach_bo() has been improved to properly unwind and propagate errors, eliminating silent failure conditions that could compound existing issues. Additionally, the fix removes reliance on the previous detach mechanism that required both contexts to be attached before cleanup, instead implementing direct context clearing through xe_migrate_ccs_rw_copy_clear(). This change ensures proper resource management regardless of partial attachment states. The solution aligns with industry best practices for concurrent programming and memory management in kernel space, addressing fundamental synchronization issues that could otherwise lead to system crashes or data corruption during high-intensity graphics operations.
The fix demonstrates proper adherence to kernel security principles by ensuring atomicity and consistency in buffer object state transitions while maintaining proper resource lifecycle management. By implementing pre-submission attachment and post-fence detachment, the solution prevents the conditions that could allow VF migration events to observe inconsistent memory states. This approach follows established patterns for managing shared resources in concurrent systems and reduces the attack surface for potential exploitation of timing-based vulnerabilities. The cherry-pick from commit d45ad0aa7a1eb5d7288b5ed948b05695611dc39e indicates this fix was part of a broader security update effort, suggesting similar issues may have existed in other graphics driver implementations that required similar synchronization improvements.