CVE-2026-63884 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/i915: Fix potential UAF in TTM object purge
TLDR: The bo->ttm object might be changed by calling ttm_bo_validate(), move casting it to an i915_tt object later to actually get the right pointer.
A user reported hitting the following bug under heavy use on DG2:
[26620.095550] Oops: general protection fault, probably for non-canonical address 0xa56b6b6b6b6b6b8b: 0000 1 SMP NOPTI
[26620.095556] CPU: 2 UID: 0 PID: 631 Comm: Xorg Not tainted 6.18.8 #1 PREEMPT(lazy)
[26620.095558] Hardware name: ASRock B850M Steel Legend WiFi/B850M Steel Legend WiFi, BIOS 3.50 09/18/2025
[26620.095559] RIP: 0010:i915_ttm_purge+0x84/0x100 [i915]
[26620.095604] Code: 00 00 00 48 8d 54 24 10 48 89 e6 48 89 fb e8 83 aa ae ff 85 c0 75 6f 48 83 bb a8 01 00 00 00 74 2c 48 8b 45 78 48 85 c0 74 23 <48> 8b 78 20 48 c7 c2 ff ff ff ff 31 f6 e8 7a 73 e3 e0 48 8b 7d 78
[26620.095605] RSP: 0018:ffffc90005fd7430 EFLAGS: 00010282
[26620.095607] RAX: a56b6b6b6b6b6b6b RBX: ffff8881f46c3dc0 RCX: 0000000000000000
[26620.095608] RDX: 0000000000000000 RSI: 0000000000000246 RDI: 00000000ffffffff
[26620.095609] RBP: ffff888289610f00 R08: 0000000000000001 R09: ffff88823b022000
[26620.095609] R10: ffff888103029b28 R11: ffff8881fc7f3800 R12: ffff88810b6150d0
[26620.095609] R13: ffff888289610f00 R14: 0000000000000000 R15: ffff8881f46c3dc0
[26620.095610] FS: 00007f1004d86900(0000) GS:ffff88901c858000(0000) knlGS:0000000000000000
[26620.095611] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[26620.095611] CR2: 00007f0fdf489000 CR3: 000000035b0c1000 CR4: 0000000000750ef0
[26620.095612] PKRU: 55555554
[26620.095612] Call Trace:
[26620.095615] <TASK>
[26620.095615] i915_ttm_move+0x2b9/0x420 [i915]
[26620.095642] ? ttm_tt_init+0x65/0x80 [ttm]
[26620.095644] ? i915_ttm_tt_create+0xc6/0x150 [i915]
[26620.095667] ttm_bo_handle_move_mem+0xb6/0x160 [ttm]
[26620.095669] ttm_bo_evict+0x100/0x150 [ttm]
[26620.095671] ? preempt_count_add+0x64/0xa0
[26620.095673] ? _raw_spin_lock+0xe/0x30
[26620.095675] ? _raw_spin_unlock+0xd/0x30
[26620.095675] ? i915_gem_object_evictable+0xb7/0xd0 [i915]
[26620.095704] ttm_bo_evict_cb+0x6e/0xd0 [ttm]
[26620.095705] ttm_lru_walk_for_evict+0xa6/0x200 [ttm]
[26620.095708] ttm_bo_alloc_resource+0x185/0x4f0 [ttm]
[26620.095709] ? init_object+0x62/0xd0
[26620.095712] ttm_bo_validate+0x7a/0x180 [ttm]
[26620.095713] ? _raw_spin_unlock_irqrestore+0x16/0x30
[26620.095714] __i915_ttm_get_pages+0xb0/0x170 [i915]
[26620.095737] i915_ttm_get_pages+0x9f/0x150 [i915]
[26620.095759] ? i915_gem_do_execbuffer+0xedc/0x2b40 [i915]
[26620.095786] ? alloc_debug_processing+0xd0/0x100
[26620.095787] ? _raw_spin_unlock_irqrestore+0x16/0x30
[26620.095788] ? i915_vma_instance+0xa0/0x4e0 [i915]
[26620.095822] __i915_gem_object_get_pages+0x2f/0x40 [i915]
[26620.095848] i915_vma_pin_ww+0x706/0x980 [i915]
[26620.095875] ? i915_gem_do_execbuffer+0xedc/0x2b40 [i915]
[26620.095904] eb_validate_vmas+0x170/0xa00 [i915]
[26620.095930] i915_gem_do_execbuffer+0x1201/0x2b40 [i915]
[26620.095953] ? alloc_debug_processing+0xd0/0x100
[26620.095954] ? _raw_spin_unlock_irqrestore+0x16/0x30
[26620.095955] ? i915_gem_execbuffer2_ioctl+0xc9/0x240 [i915]
[26620.095977] ? __wake_up_sync_key+0x32/0x50
[26620.095979] ? i915_gem_execbuffer2_ioctl+0xc9/0x240 [i915]
[26620.096001] ? __slab_alloc.isra.0+0x67/0xc0
[26620.096003] i915_gem_execbuffer2_ioctl+0x11a/0x240 [i915]
Results from decode_stacktrace.sh pointed to dereference of a file pointer field of a i915 TTM page vector container associated with an object being purged on eviction. That path is taken when the object is marked as no longer needed.
Code analysis revealed a possibility of the i915 TTM page vector container being replaced with a new instance inside a function that purges content of the object, should it be still busy. That function is called, indirectly via a more general function that changes the object's placement and caching policy, ---truncated---
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability in question resides within the Linux kernel's graphics subsystem, specifically affecting the intel i915 driver's interaction with the TTM (Translation Table Manager) layer. This issue manifests as a potential use-after-free condition during the purging of TTM objects, which can lead to system crashes and potentially arbitrary code execution. The flaw occurs when a graphics object is being evicted from memory while still in use or undergoing processing, causing an inconsistent state where the object reference becomes invalid before it is properly dereferenced.
The technical root cause stems from improper handling of object references during the TTM validation process. When ttm_bo_validate() is invoked to update an object's placement or caching attributes, it may replace the existing TTM object with a new instance. However, prior to this replacement, the code path attempts to cast and dereference the original object pointer into an i915_tt structure without ensuring that the reference remains valid throughout the operation. This race condition allows for a scenario where memory that was freed or reallocated is still being accessed, resulting in the general protection fault observed in the kernel crash dump.
The operational impact of this vulnerability is significant within graphics-intensive environments such as desktop compositors and GPU-accelerated applications. The crash occurs under heavy usage conditions on DG2 hardware, indicating that concurrent access patterns and memory pressure exacerbate the problem. The stack trace shows the fault propagates through multiple layers including TTM's eviction mechanisms, i915's page management functions, and eventually reaches the graphics execution buffer processing path. This demonstrates how the vulnerability can affect core graphics functionality and potentially compromise system stability during normal operations.
This vulnerability aligns with CWE-416 Use After Free, which classifies the improper deallocation of memory followed by its subsequent access. The attack surface is consistent with the ATT&CK technique T1547.001 Account Manipulation, as the vulnerability could potentially be exploited to gain elevated privileges through kernel-level memory corruption. The fix implemented addresses the core issue by ensuring proper synchronization and reference validation before casting to the i915_tt structure, thereby preventing the invalid pointer dereference that leads to system crashes. Mitigation efforts should include applying the patched kernel version immediately, as the vulnerability affects graphics drivers used in both desktop and server environments where GPU acceleration is prevalent.