[PATCH V1] iommu/sva: Fix crash in iommu_sva_unbind_device()

[Lizhi Hou]

domain->mm->iommu_mm can be freed by iommu_domain_free():
  iommu_domain_free()
    mmdrop()
      __mmdrop()
        mm_pasid_drop()
After iommu_domain_free() returns, accessing domain->mm->iommu_mm may
dereference a freed mm structure, leading to a crash.

Fix this by taking a reference to the mm via mmgrab() before
calling iommu_domain_free(), and dropping it with mmdrop() after
finishing access to domain->mm->iommu_mm.

Fixes: e37d5a2d60a3 ("iommu/sva: invalidate stale IOTLB entries for kernel address space")
Signed-off-by: Lizhi Hou <lizhi.hou@xxxxxxx>
---
 drivers/iommu/iommu-sva.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
index 07d64908a05f..523b8c65c86f 100644
--- a/drivers/iommu/iommu-sva.c
+++ b/drivers/iommu/iommu-sva.c
@@ -179,6 +179,7 @@ void iommu_sva_unbind_device(struct iommu_sva *handle)
 		return;
 	}
 
+	mmgrab(domain->mm);
 	iommu_detach_device_pasid(domain, dev, iommu_mm->pasid);
 	if (--domain->users == 0) {
 		list_del(&domain->next);
@@ -190,6 +191,7 @@ void iommu_sva_unbind_device(struct iommu_sva *handle)
 		if (list_empty(&iommu_sva_mms))
 			iommu_sva_present = false;
 	}
+	mmdrop(domain->mm);
 
 	mutex_unlock(&iommu_sva_lock);
 	kfree(handle);
-- 
2.34.1