From: Chris Wilson chris@chris-wilson.co.uk
commit 2abaad4eb59d1cdc903ea84c06acb406e2fbb263 upstream.
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 chris@chris-wilson.co.uk Cc: Tvrtko Ursulin tvrtko.ursulin@intel.com Cc: stable@vger.kernel.org # v5.6+ Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20200427093038.29219-1-chris@c... (cherry picked from commit 2759e395358b2b909577928894f856ab75bea41a) Signed-off-by: Rodrigo Vivi rodrigo.vivi@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/gpu/drm/i915/gt/intel_timeline.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/drivers/gpu/drm/i915/gt/intel_timeline.c +++ b/drivers/gpu/drm/i915/gt/intel_timeline.c @@ -519,6 +519,8 @@ int intel_timeline_read_hwsp(struct i915
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)))