drm/amdgpu: fix a job->pasid access race in gpu recovery

Avoid a possible UAF in GPU recovery due to a race between
the sched timeout callback and the tdr work queue.

The gpu recovery function calls drm_sched_stop() and
later drm_sched_start(). drm_sched_start() restarts
the tdr queue which will eventually free the job. If
the tdr queue frees the job before time out callback
completes, the job will be freed and we'll get a UAF
when accessing the pasid. Cache it early to avoid the
UAF.

Example KASAN trace:
[ 493.058141] BUG: KASAN: slab-use-after-free in amdgpu_device_gpu_recover+0x968/0x990 [amdgpu]
[ 493.067530] Read of size 4 at addr ffff88b0ce3f794c by task kworker/u128:1/323
[ 493.074892]
[ 493.076485] CPU: 9 UID: 0 PID: 323 Comm: kworker/u128:1 Tainted: G E 6.16.0-1289896.2.zuul.bf4f11df81c1410bbe901c4373305a31 #1 PREEMPT(voluntary)
[ 493.076493] Tainted: [E]=UNSIGNED_MODULE
[ 493.076495] Hardware name: TYAN B8021G88V2HR-2T/S8021GM2NR-2T, BIOS V1.03.B10 04/01/2019
[ 493.076500] Workqueue: amdgpu-reset-dev drm_sched_job_timedout [gpu_sched]
[ 493.076512] Call Trace:
[ 493.076515] <TASK>
[ 493.076518] dump_stack_lvl+0x64/0x80
[ 493.076529] print_report+0xce/0x630
[ 493.076536] ? _raw_spin_lock_irqsave+0x86/0xd0
[ 493.076541] ? __pfx__raw_spin_lock_irqsave+0x10/0x10
[ 493.076545] ? amdgpu_device_gpu_recover+0x968/0x990 [amdgpu]
[ 493.077253] kasan_report+0xb8/0xf0
[ 493.077258] ? amdgpu_device_gpu_recover+0x968/0x990 [amdgpu]
[ 493.077965] amdgpu_device_gpu_recover+0x968/0x990 [amdgpu]
[ 493.078672] ? __pfx_amdgpu_device_gpu_recover+0x10/0x10 [amdgpu]
[ 493.079378] ? amdgpu_coredump+0x1fd/0x4c0 [amdgpu]
[ 493.080111] amdgpu_job_timedout+0x642/0x1400 [amdgpu]
[ 493.080903] ? pick_task_fair+0x24e/0x330
[ 493.080910] ? __pfx_amdgpu_job_timedout+0x10/0x10 [amdgpu]
[ 493.081702] ? _raw_spin_lock+0x75/0xc0
[ 493.081708] ? __pfx__raw_spin_lock+0x10/0x10
[ 493.081712] drm_sched_job_timedout+0x1b0/0x4b0 [gpu_sched]
[ 493.081721] ? __pfx__raw_spin_lock_irq+0x10/0x10
[ 493.081725] process_one_work+0x679/0xff0
[ 493.081732] worker_thread+0x6ce/0xfd0
[ 493.081736] ? __pfx_worker_thread+0x10/0x10
[ 493.081739] kthread+0x376/0x730
[ 493.081744] ? __pfx_kthread+0x10/0x10
[ 493.081748] ? __pfx__raw_spin_lock_irq+0x10/0x10
[ 493.081751] ? __pfx_kthread+0x10/0x10
[ 493.081755] ret_from_fork+0x247/0x330
[ 493.081761] ? __pfx_kthread+0x10/0x10
[ 493.081764] ret_from_fork_asm+0x1a/0x30
[ 493.081771] </TASK>

Fixes: a72002cb181f ("drm/amdgpu: Make use of drm_wedge_task_info")
Link: https://github.com/HansKristian-Work/vkd3d-proton/pull/2670
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Suggested-by: Matthew Brost <[e-mail]>
Reviewed-by: Srinivasan Shanmugam <[e-mail]>
Reviewed-by: Lijo Lazar <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>
(cherry picked from commit 20880a3fd5dd7bca1a079534cf6596bda92e107d)

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

···
 	struct amdgpu_hive_info *hive = NULL;
 	int r = 0;
 	bool need_emergency_restart = false;
+	/* save the pasid here as the job may be freed before the end of the reset */
+	int pasid = job ? job->pasid : -EINVAL;
 
 	/*
 	 * If it reaches here because of hang/timeout and a RAS error is
···
 	if (!r) {
 		struct amdgpu_task_info *ti = NULL;
 
-		if (job)
-			ti = amdgpu_vm_get_task_info_pasid(adev, job->pasid);
+		/*
+		 * The job may already be freed at this point via the sched tdr workqueue so
+		 * use the cached pasid.
+		 */
+		if (pasid >= 0)
+			ti = amdgpu_vm_get_task_info_pasid(adev, pasid);
 
 		drm_dev_wedged_event(adev_to_drm(adev), DRM_WEDGE_RECOVERY_NONE,
 				     ti ? &ti->task : NULL);