From 2abaad4eb59d1cdc903ea84c06acb406e2fbb263 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Mon, 27 Apr 2020 10:30:38 +0100 Subject: [PATCH] drm/i915/gt: Check cacheline is valid before acquiring The hwsp_cacheline pointer from i915_request is very, very flimsy. The i915_request.timeline (and the hwsp_cacheline) are lost upon retiring (after an RCU grace). Therefore we need to confirm that once we have the right pointer for the cacheline, it is not in the process of being retired and disposed of before we attempt to acquire a reference to the cacheline. <3>[ 547.208237] BUG: KASAN: use-after-free in active_debug_hint+0x6a/0x70 [i915] <3>[ 547.208366] Read of size 8 at addr ffff88822a0d2710 by task gem_exec_parall/2536 <4>[ 547.208547] CPU: 3 PID: 2536 Comm: gem_exec_parall Tainted: G U 5.7.0-rc2-ged7a286b5d02d-kasan_117+ #1 <4>[ 547.208556] Hardware name: Dell Inc. XPS 13 9350/, BIOS 1.4.12 11/30/2016 <4>[ 547.208564] Call Trace: <4>[ 547.208579] dump_stack+0x96/0xdb <4>[ 547.208707] ? active_debug_hint+0x6a/0x70 [i915] <4>[ 547.208719] print_address_description.constprop.6+0x16/0x310 <4>[ 547.208841] ? active_debug_hint+0x6a/0x70 [i915] <4>[ 547.208963] ? active_debug_hint+0x6a/0x70 [i915] <4>[ 547.208975] __kasan_report+0x137/0x190 <4>[ 547.209106] ? active_debug_hint+0x6a/0x70 [i915] <4>[ 547.209127] kasan_report+0x32/0x50 <4>[ 547.209257] ? i915_gemfs_fini+0x40/0x40 [i915] <4>[ 547.209376] active_debug_hint+0x6a/0x70 [i915] <4>[ 547.209389] debug_print_object+0xa7/0x220 <4>[ 547.209405] ? lockdep_hardirqs_on+0x348/0x5f0 <4>[ 547.209426] debug_object_assert_init+0x297/0x430 <4>[ 547.209449] ? debug_object_free+0x360/0x360 <4>[ 547.209472] ? lock_acquire+0x1ac/0x8a0 <4>[ 547.209592] ? intel_timeline_read_hwsp+0x4f/0x840 [i915] <4>[ 547.209737] ? i915_active_acquire_if_busy+0x66/0x120 [i915] <4>[ 547.209861] i915_active_acquire_if_busy+0x66/0x120 [i915] <4>[ 547.209990] ? __live_alloc.isra.15+0xc0/0xc0 [i915] <4>[ 547.210005] ? rcu_read_lock_sched_held+0xd0/0xd0 <4>[ 547.210017] ? print_usage_bug+0x580/0x580 <4>[ 547.210153] intel_timeline_read_hwsp+0xbc/0x840 [i915] <4>[ 547.210284] __emit_semaphore_wait+0xd5/0x480 [i915] <4>[ 547.210415] ? i915_fence_get_timeline_name+0x110/0x110 [i915] <4>[ 547.210428] ? lockdep_hardirqs_on+0x348/0x5f0 <4>[ 547.210442] ? _raw_spin_unlock_irq+0x2a/0x40 <4>[ 547.210567] ? __await_execution.constprop.51+0x2e0/0x570 [i915] <4>[ 547.210706] i915_request_await_dma_fence+0x8f7/0xc70 [i915] Fixes: 85bedbf191e8 ("drm/i915/gt: Eliminate the trylock for reading a timeline's hwsp") Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Cc: # v5.6+ Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20200427093038.29219-1-chris@chris-wilson.co.uk (cherry picked from commit 2759e395358b2b909577928894f856ab75bea41a) Signed-off-by: Rodrigo Vivi --- drivers/gpu/drm/i915/gt/intel_timeline.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c b/drivers/gpu/drm/i915/gt/intel_timeline.c index 91debbc97c9a..08b56d7ab4f4 100644 --- a/drivers/gpu/drm/i915/gt/intel_timeline.c +++ b/drivers/gpu/drm/i915/gt/intel_timeline.c @@ -521,6 +521,8 @@ int intel_timeline_read_hwsp(struct i915_request *from, rcu_read_lock(); cl = rcu_dereference(from->hwsp_cacheline); + if (i915_request_completed(from)) /* confirm cacheline is valid */ + goto unlock; if (unlikely(!i915_active_acquire_if_busy(&cl->active))) goto unlock; /* seqno wrapped and completed! */ if (unlikely(i915_request_completed(from))) -- 2.30.2