iommu/vt-d: Fix general protection fault in aux_detach_device()

The aux-domain attach/detach are not tracked, some data structures might
be used after free. This causes general protection faults when multiple
subdevices are created and assigned to a same guest machine:

| general protection fault, probably for non-canonical address 0xdead000000000100: 0000 [#1] SMP NOPTI
| RIP: 0010:intel_iommu_aux_detach_device+0x12a/0x1f0
| [...]
| Call Trace:
| iommu_aux_detach_device+0x24/0x70
| vfio_mdev_detach_domain+0x3b/0x60
| ? vfio_mdev_set_domain+0x50/0x50
| iommu_group_for_each_dev+0x4f/0x80
| vfio_iommu_detach_group.isra.0+0x22/0x30
| vfio_iommu_type1_detach_group.cold+0x71/0x211
| ? find_exported_symbol_in_section+0x4a/0xd0
| ? each_symbol_section+0x28/0x50
| __vfio_group_unset_container+0x4d/0x150
| vfio_group_try_dissolve_container+0x25/0x30
| vfio_group_put_external_user+0x13/0x20
| kvm_vfio_group_put_external_user+0x27/0x40 [kvm]
| kvm_vfio_destroy+0x45/0xb0 [kvm]
| kvm_put_kvm+0x1bb/0x2e0 [kvm]
| kvm_vm_release+0x22/0x30 [kvm]
| __fput+0xcc/0x260
| ____fput+0xe/0x10
| task_work_run+0x8f/0xb0
| do_exit+0x358/0xaf0
| ? wake_up_state+0x10/0x20
| ? signal_wake_up_state+0x1a/0x30
| do_group_exit+0x47/0xb0
| __x64_sys_exit_group+0x18/0x20
| do_syscall_64+0x57/0x1d0
| entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fix the crash by tracking the subdevices when attaching and detaching
aux-domains.

Fixes: 67b8e02b5e76 ("iommu/vt-d: Aux-domain specific domain attach/detach")
Co-developed-by: Xin Zeng <[e-mail]>
Signed-off-by: Xin Zeng <[e-mail]>
Signed-off-by: Liu Yi L <[e-mail]>
Acked-by: Lu Baolu <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

drivers/iommu/intel/iommu.c

···
 		domain->flags |= DOMAIN_FLAG_USE_FIRST_LEVEL;
 	domain->has_iotlb_device = false;
 	INIT_LIST_HEAD(&domain->devices);
+	INIT_LIST_HEAD(&domain->subdevices);
 
 	return domain;
 }
···
 	info->iommu = iommu;
 	info->pasid_table = NULL;
 	info->auxd_enabled = 0;
-	INIT_LIST_HEAD(&info->auxiliary_domains);
+	INIT_LIST_HEAD(&info->subdevices);
 
 	if (dev && dev_is_pci(dev)) {
 		struct pci_dev *pdev = to_pci_dev(info->dev);
···
 			domain->type == IOMMU_DOMAIN_UNMANAGED;
 }
 
-static void auxiliary_link_device(struct dmar_domain *domain,
-				  struct device *dev)
+static inline struct subdev_domain_info *
+lookup_subdev_info(struct dmar_domain *domain, struct device *dev)
 {
-	struct device_domain_info *info = get_domain_info(dev);
+	struct subdev_domain_info *sinfo;
 
-	assert_spin_locked(&device_domain_lock);
-	if (WARN_ON(!info))
-		return;
+	if (!list_empty(&domain->subdevices)) {
+		list_for_each_entry(sinfo, &domain->subdevices, link_domain) {
+			if (sinfo->pdev == dev)
+				return sinfo;
+		}
+	}
 
-	domain->auxd_refcnt++;
-	list_add(&domain->auxd, &info->auxiliary_domains);
+	return NULL;
 }
 
-static void auxiliary_unlink_device(struct dmar_domain *domain,
-				    struct device *dev)
+static int auxiliary_link_device(struct dmar_domain *domain,
+				 struct device *dev)
 {
 	struct device_domain_info *info = get_domain_info(dev);
+	struct subdev_domain_info *sinfo = lookup_subdev_info(domain, dev);
 
 	assert_spin_locked(&device_domain_lock);
 	if (WARN_ON(!info))
-		return;
+		return -EINVAL;
 
-	list_del(&domain->auxd);
-	domain->auxd_refcnt--;
+	if (!sinfo) {
+		sinfo = kzalloc(sizeof(*sinfo), GFP_ATOMIC);
+		sinfo->domain = domain;
+		sinfo->pdev = dev;
+		list_add(&sinfo->link_phys, &info->subdevices);
+		list_add(&sinfo->link_domain, &domain->subdevices);
+	}
 
-	if (!domain->auxd_refcnt && domain->default_pasid > 0)
-		ioasid_put(domain->default_pasid);
+	return ++sinfo->users;
+}
+
+static int auxiliary_unlink_device(struct dmar_domain *domain,
+				   struct device *dev)
+{
+	struct device_domain_info *info = get_domain_info(dev);
+	struct subdev_domain_info *sinfo = lookup_subdev_info(domain, dev);
+	int ret;
+
+	assert_spin_locked(&device_domain_lock);
+	if (WARN_ON(!info || !sinfo || sinfo->users <= 0))
+		return -EINVAL;
+
+	ret = --sinfo->users;
+	if (!ret) {
+		list_del(&sinfo->link_phys);
+		list_del(&sinfo->link_domain);
+		kfree(sinfo);
+	}
+
+	return ret;
 }
 
 static int aux_domain_add_dev(struct dmar_domain *domain,
···
 	}
 
 	spin_lock_irqsave(&device_domain_lock, flags);
+	ret = auxiliary_link_device(domain, dev);
+	if (ret <= 0)
+		goto link_failed;
+
+	/*
+	 * Subdevices from the same physical device can be attached to the
+	 * same domain. For such cases, only the first subdevice attachment
+	 * needs to go through the full steps in this function. So if ret >
+	 * 1, just goto out.
+	 */
+	if (ret > 1)
+		goto out;
+
 	/*
 	 * iommu->lock must be held to attach domain to iommu and setup the
 	 * pasid entry for second level translation.
···
 						     domain->default_pasid);
 	if (ret)
 		goto table_failed;
+
 	spin_unlock(&iommu->lock);
-
-	auxiliary_link_device(domain, dev);
-
+out:
 	spin_unlock_irqrestore(&device_domain_lock, flags);
 
 	return 0;
···
 	domain_detach_iommu(domain, iommu);
 attach_failed:
 	spin_unlock(&iommu->lock);
+	auxiliary_unlink_device(domain, dev);
+link_failed:
 	spin_unlock_irqrestore(&device_domain_lock, flags);
-	if (!domain->auxd_refcnt && domain->default_pasid > 0)
+	if (list_empty(&domain->subdevices) && domain->default_pasid > 0)
 		ioasid_put(domain->default_pasid);
 
 	return ret;
···
 	info = get_domain_info(dev);
 	iommu = info->iommu;
 
-	auxiliary_unlink_device(domain, dev);
-
-	spin_lock(&iommu->lock);
-	intel_pasid_tear_down_entry(iommu, dev, domain->default_pasid, false);
-	domain_detach_iommu(domain, iommu);
-	spin_unlock(&iommu->lock);
+	if (!auxiliary_unlink_device(domain, dev)) {
+		spin_lock(&iommu->lock);
+		intel_pasid_tear_down_entry(iommu, dev,
+					    domain->default_pasid, false);
+		domain_detach_iommu(domain, iommu);
+		spin_unlock(&iommu->lock);
+	}
 
 	spin_unlock_irqrestore(&device_domain_lock, flags);
+
+	if (list_empty(&domain->subdevices) && domain->default_pasid > 0)
+		ioasid_put(domain->default_pasid);
 }
 
 static int prepare_domain_attach_device(struct iommu_domain *domain,

include/linux/intel-iommu.h

···
 					/* Domain ids per IOMMU. Use u16 since
 					 * domain ids are 16 bit wide according
 					 * to VT-d spec, section 9.3 */
-	unsigned int	auxd_refcnt;	/* Refcount of auxiliary attaching */
 
 	bool has_iotlb_device;
 	struct list_head devices;	/* all devices' list */
-	struct list_head auxd;		/* link to device's auxiliary list */
+	struct list_head subdevices;	/* all subdevices' list */
 	struct iova_domain iovad;	/* iova's that belong to this domain */
 
 	struct dma_pte	*pgd;		/* virtual address */
···
 	struct dmar_drhd_unit *drhd;
 };
 
+/* Per subdevice private data */
+struct subdev_domain_info {
+	struct list_head link_phys;	/* link to phys device siblings */
+	struct list_head link_domain;	/* link to domain siblings */
+	struct device *pdev;		/* physical device derived from */
+	struct dmar_domain *domain;	/* aux-domain */
+	int users;			/* user count */
+};
+
 /* PCI domain-device relationship */
 struct device_domain_info {
 	struct list_head link;	/* link to domain siblings */
 	struct list_head global; /* link to global list */
 	struct list_head table;	/* link to pasid table */
-	struct list_head auxiliary_domains; /* auxiliary domains
-					     * attached to this device
-					     */
+	struct list_head subdevices; /* subdevices sibling */
 	u32 segment;		/* PCI segment number */
 	u8 bus;			/* PCI bus number */
 	u8 devfn;		/* PCI devfn number */