We easily hit drm/i915 panic on TGL when running glmark2, and finally
caught the race condition of use-after-free with enabling KASAN.
The call stack is below:
===
[ 534.472675] BUG: KASAN: use-after-free in __i915_active_fence_set+0x26d/0x3d0 [i915]
[ 534.472679] Write of size 8 at addr ffff8883f0372388 by task glmark2/3199
[ 534.472684] CPU: 3 PID: 3199 Comm: glmark2 Tainted: G U E 5.4.0-rc8 #8
[ 534.472687] Call Trace:
[ 534.472693] dump_stack+0x95/0xd5
[ 534.472722] ? __i915_active_fence_set+0x26d/0x3d0 [i915]
[ 534.472727] print_address_description.constprop.5+0x20/0x320
[ 534.472751] ? __i915_active_fence_set+0x26d/0x3d0 [i915]
[ 534.472792] ? __i915_active_fence_set+0x26d/0x3d0 [i915]
[ 534.472794] __kasan_report+0x149/0x18c
[ 534.472798] ? _raw_spin_lock+0x1/0xd0
[ 534.472820] ? __i915_active_fence_set+0x26d/0x3d0 [i915]
[ 534.472822] kasan_report+0x12/0x20
[ 534.472825] __asan_report_store8_noabort+0x17/0x20
[ 534.472847] __i915_active_fence_set+0x26d/0x3d0 [i915]
[ 534.472870] i915_active_ref+0x2c8/0x530 [i915]
[ 534.472874] ? dma_resv_add_shared_fence+0x291/0x460
[ 534.472902] __i915_vma_move_to_active+0x56/0x70 [i915]
[ 534.472927] i915_vma_move_to_active+0x54/0x420 [i915]
[ 534.472931] ? mutex_unlock+0x22/0x40
[ 534.472957] i915_gem_do_execbuffer+0x1d45/0x3e20 [i915]
[ 534.472959] ? __kmalloc_node+0x12c/0x350
[ 534.472983] ? eb_relocate_slow+0xb40/0xb40 [i915]
[ 534.472985] ? _raw_write_trylock+0x110/0x110
[ 534.472987] ? get_partial_node.isra.72+0x51/0x260
[ 534.472991] ? unix_stream_read_generic+0x583/0x1a80
[ 534.472994] ? ___slab_alloc+0x1d8/0x550
[ 534.472998] ? kvmalloc_node+0x31/0x80
[ 534.473000] ? kasan_unpoison_shadow+0x35/0x50
[ 534.473002] ? _raw_spin_lock+0x7b/0xd0
[ 534.473004] ? radix_tree_lookup+0xd/0x10
[ 534.473006] ? idr_find+0x3b/0x60
[ 534.473029] i915_gem_execbuffer2_ioctl+0x634/0x8a0 [i915]
[ 534.473052] ? i915_gem_execbuffer_ioctl+0xd50/0xd50 [i915]
[ 534.473054] ? unix_stream_recvmsg+0x97/0xd0
[ 534.473056] ? unix_stream_splice_read+0x1c0/0x1c0
[ 534.473058] ? __unix_insert_socket+0x180/0x180
[ 534.473081] ? i915_gem_execbuffer_ioctl+0xd50/0xd50 [i915]
[ 534.473094] drm_ioctl_kernel+0x1ed/0x2b0 [drm]
[ 534.473103] ? drm_setversion+0x8c0/0x8c0 [drm]
[ 534.473106] ? __kasan_check_write+0x14/0x20
[ 534.473115] drm_ioctl+0x68b/0xaa0 [drm]
...
[ 534.473239] Allocated by task 3199:
[ 534.473241] save_stack+0x21/0x90
[ 534.473243] __kasan_kmalloc.constprop.8+0xa7/0xd0
[ 534.473245] kasan_slab_alloc+0x11/0x20
[ 534.473246] kmem_cache_alloc+0xce/0x240
[ 534.473273] i915_active_ref+0xc2/0x530 [i915]
[ 534.473302] __i915_vma_move_to_active+0x56/0x70 [i915]
[ 534.473328] i915_vma_move_to_active+0x54/0x420 [i915]
[ 534.473355] i915_gem_do_execbuffer+0x1d45/0x3e20 [i915]
[ 534.473381] i915_gem_execbuffer2_ioctl+0x634/0x8a0 [i915]
[ 534.473392] drm_ioctl_kernel+0x1ed/0x2b0 [drm]
[ 534.473402] drm_ioctl+0x68b/0xaa0 [drm]
[ 534.473404] do_vfs_ioctl+0x19a/0xf10
[ 534.473405] ksys_ioctl+0x75/0x80
[ 534.473407] __x64_sys_ioctl+0x73/0xb0
[ 534.473408] do_syscall_64+0x9f/0x3a0
[ 534.473410] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 534.473412] Freed by task 0:
[ 534.473414] save_stack+0x21/0x90
[ 534.473415] __kasan_slab_free+0x137/0x190
[ 534.473417] kasan_slab_free+0xe/0x10
[ 534.473418] kmem_cache_free+0xeb/0x2c0
[ 534.473444] __active_retire+0x1f2/0x240 [i915]
[ 534.473471] active_retire+0x13b/0x1b0 [i915]
[ 534.473496] node_retire+0x54/0x80 [i915]
[ 534.473523] intel_engine_breadcrumbs_irq+0x5f0/0xd10 [i915]
[ 534.473549] cs_irq_handler+0x66/0xb0 [i915]
[ 534.473575] gen11_gt_irq_handler+0x26c/0x400 [i915]
[ 534.473600] gen11_irq_handler+0xc3/0x250 [i915]
[ 534.473603] __handle_irq_event_percpu+0xe0/0x4c0
[ 534.473605] handle_irq_event_percpu+0x71/0x140
[ 534.473606] handle_irq_event+0xad/0x140
[ 534.473608] handle_edge_irq+0x1f6/0x780
[ 534.473610] do_IRQ+0x9f/0x1f0
[ 534.473612] The buggy address belongs to the object at ffff8883f0372380
which belongs to the cache active_node of size 72
[ 534.473615] The buggy address is located 8 bytes inside of
===
The race scenerio is like:
Initially ref->count is 1, interrupt handler is trying to free the
node.
===
CPUA in interrupt context CPUB in i915_gem_execbuffer2_ioctl
__active_retire -->
spin_lock(&ref->tree_lock)
decrease ref->count to 0
i915_active_ref -->
increase ref->count to 1
(i915_active_acquire)
get the dirty ref->cache
(READ_ONCE(ref->cache))
return the dirty node
set ref->cache to NULL
spin_unlock(&ref->tree_lock)
free the node
hit use-after-free in
__i915_active_fence_set()
===
Here we need to use spinlock ref->tree_lock to protect the access
of READ_ONCE(ref->cache), then the race scenerio can be resolved.
with this patch, it passed our stress test for a very long time.
Signed-off-by: Chuansheng Liu <chuansheng.liu@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_active.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
index dca15ace88f6..3d68b910e949 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -214,7 +214,10 @@ active_instance(struct i915_active *ref, struct intel_timeline *tl)
* after the previous activity has been retired, or if it matches the
* current timeline.
*/
+ spin_lock_irq(&ref->tree_lock);
node = READ_ONCE(ref->cache);
+ spin_unlock_irq(&ref->tree_lock);
+
if (node && node->timeline == idx)
return &node->base;
--
2.17.1
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