iommu/vt-d: Fix UAF on sva unbind with pending IOPFs

Commit 17fce9d ("iommu/vt-d: Put iopf enablement in domain attach
path") disables IOPF on device by removing the device from its IOMMU's
IOPF queue when the last IOPF-capable domain is detached from the device.
Unfortunately, it did this in a wrong place where there are still pending
IOPFs. As a result, a use-after-free error is potentially triggered and
eventually a kernel panic with a kernel trace similar to the following:

 refcount_t: underflow; use-after-free.
 WARNING: CPU: 3 PID: 313 at lib/refcount.c:28 refcount_warn_saturate+0xd8/0xe0
 Workqueue: iopf_queue/dmar0-iopfq iommu_sva_handle_iopf
 Call Trace:
   <TASK>
   iopf_free_group+0xe/0x20
   process_one_work+0x197/0x3d0
   worker_thread+0x23a/0x350
   ? rescuer_thread+0x4a0/0x4a0
   kthread+0xf8/0x230
   ? finish_task_switch.isra.0+0x81/0x260
   ? kthreads_online_cpu+0x110/0x110
   ? kthreads_online_cpu+0x110/0x110
   ret_from_fork+0x13b/0x170
   ? kthreads_online_cpu+0x110/0x110
   ret_from_fork_asm+0x11/0x20
   </TASK>
  ---[ end trace 0000000000000000 ]---

The intel_pasid_tear_down_entry() function is responsible for blocking
hardware from generating new page faults and flushing all in-flight
ones. Therefore, moving iopf_for_domain_remove() after this function
should resolve this.

Fixes: 17fce9d ("iommu/vt-d: Put iopf enablement in domain attach path")
Reported-by: Ethan Milon <[email protected]>
Closes: https://lore.kernel.org/r/[email protected]
Suggested-by: Ethan Milon <[email protected]>
Signed-off-by: Lu Baolu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: LuBaolu

drivers/iommu/intel/iommu.c

@@ -4081,8 +4081,8 @@ static int blocking_domain_set_dev_pasid(struct iommu_domain *domain,
 {
 	struct device_domain_info *info = dev_iommu_priv_get(dev);
 
-	iopf_for_domain_remove(old, dev);
 	intel_pasid_tear_down_entry(info->iommu, dev, pasid, false);
+	iopf_for_domain_remove(old, dev);
 	domain_remove_dev_pasid(old, dev, pasid);
 
 	return 0;