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* [PATCH v2] drm/i915: Fix potential UAF in TTM object purge
@ 2026-05-08 12:23 Janusz Krzysztofik
  2026-05-08 12:32 ` Christian König
                   ` (3 more replies)
  0 siblings, 4 replies; 5+ messages in thread
From: Janusz Krzysztofik @ 2026-05-08 12:23 UTC (permalink / raw)
  To: intel-gfx
  Cc: dri-devel, Jani Nikula, Joonas Lahtinen, Rodrigo Vivi,
	Tvrtko Ursulin, Christian König, Matthew Auld,
	Thomas Hellström, Andi Shyti, Krzysztof Karas,
	Krzysztof Niemiec, Sebastian Brzezinka, Janusz Krzysztofik

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, before the problematic dereference, but still after
a pointer to the container is captured, rendering the pointer no longer
valid.

Fix the issue by capturing the pointer to the container only after its
potential replacement.

v2: Move the container_of() inside the if block (Sebastian),
  - a simplified version of the commit description that explains briefly
    why the change is necessary (Christian).

Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/14882
Fixes: 7ae034590ceae ("drm/i915/ttm: add tt shmem backend")
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Cc: stable@vger.kernel.org # v5.17+
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
Cc: Sebastian Brzezinka <sebastian.brzezinka@intel.com>
Cc: "Christian König" <christian.koenig@amd.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 28 ++++++++++++++-----------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
index de70517b4ef22..df3fcc2b1248e 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
@@ -419,8 +419,6 @@ void i915_ttm_free_cached_io_rsgt(struct drm_i915_gem_object *obj)
 int i915_ttm_purge(struct drm_i915_gem_object *obj)
 {
 	struct ttm_buffer_object *bo = i915_gem_to_ttm(obj);
-	struct i915_ttm_tt *i915_tt =
-		container_of(bo->ttm, typeof(*i915_tt), ttm);
 	struct ttm_operation_ctx ctx = {
 		.interruptible = true,
 		.no_wait_gpu = false,
@@ -435,16 +433,22 @@ int i915_ttm_purge(struct drm_i915_gem_object *obj)
 	if (ret)
 		return ret;
 
-	if (bo->ttm && i915_tt->filp) {
-		/*
-		 * The below fput(which eventually calls shmem_truncate) might
-		 * be delayed by worker, so when directly called to purge the
-		 * pages(like by the shrinker) we should try to be more
-		 * aggressive and release the pages immediately.
-		 */
-		shmem_truncate_range(file_inode(i915_tt->filp),
-				     0, (loff_t)-1);
-		fput(fetch_and_zero(&i915_tt->filp));
+	if (bo->ttm) {
+		struct i915_ttm_tt *i915_tt =
+			container_of(bo->ttm, typeof(*i915_tt), ttm);
+
+		if (i915_tt->filp) {
+			/*
+			 * The below fput(which eventually calls shmem_truncate)
+			 * might be delayed by worker, so when directly called
+			 * to purge the pages(like by the shrinker) we should
+			 * try to be more aggressive and release the pages
+			 * immediately.
+			 */
+			shmem_truncate_range(file_inode(i915_tt->filp),
+					     0, (loff_t)-1);
+			fput(fetch_and_zero(&i915_tt->filp));
+		}
 	}
 
 	obj->write_domain = 0;
-- 
2.53.0


^ permalink raw reply related	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2026-05-09 13:22 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
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2026-05-08 12:23 [PATCH v2] drm/i915: Fix potential UAF in TTM object purge Janusz Krzysztofik
2026-05-08 12:32 ` Christian König
2026-05-08 12:34 ` Andi Shyti
2026-05-08 16:13 ` ✓ i915.CI.BAT: success for drm/i915: Fix potential UAF in TTM object purge (rev2) Patchwork
2026-05-09 13:22 ` ✓ i915.CI.Full: " Patchwork

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