iommu/s390: Implement blocking domain

This fixes a crash when surprise hot-unplugging a PCI device. This crash happens because during hot-unplug __iommu_group_set_domain_nofail() attaching the default domain fails when the platform no longer recognizes the device as it has already been removed and we end up with

a NULL domain pointer and UAF. This is exactly the case referred to in the second comment in __iommu_device_set_domain() and just as stated there if we can instead attach the blocking domain the UAF is prevented as this can handle the already removed device. Implement the blocking domain to use this handling. With this change, the crash is fixed but we still hit a warning attempting to change DMA ownership on a blocked device.

Fixes c76c067e488c ("s390/pci: Use dma-iommu layer")

Co-developed-by Niklas Schnelle <[email protected]>

Signed-off-by Niklas Schnelle <[email protected]>

Signed-off-by Matthew Rosato <[email protected]>

---
Changes for v4:
- fix lockdep assert
Changes for v3:
- make blocking_domain type iommu_domain
- change zdev->s390_domain to type iommu_domain and remove most uses
- remove s390_iommu_detach_device, use blocking domain attach
- add spinlock to serialize zdev->s390_domain change / access to counters

---
 arch/s390/include/asm/pci.h |  4 +-
 arch/s390/pci/pci.c         |  3 ++
 arch/s390/pci/pci_debug.c   | 10 ++++-
 drivers/iommu/s390-iommu.c  | 73 +++++++++++++++++++++++--------------
 4 files changed, 59 insertions(+), 31 deletions(-)

arch/s390/include/asm/pci.h +0 -1

index 30820a649e6e..a60a291fbd58 100644
@@ -96,7 +96,6 @@ struct zpci_bar_struct {
 	u8		size;		/* order 2 exponent */
 };
 
-struct s390_domain;
 struct kvm_zdev;
 
 #define ZPCI_FUNCTIONS_PER_BUS 256

@@ -181,9 +180,10 @@ struct zpci_dev {
 	struct dentry	*debugfs_dev;

static inline unsigned int calc_rtx(dma_addr_t ptr) {

arch/s390/include/asm/pci.h +17 -3

 	return ((unsigned long)ptr >> ZPCI_RT_SHIFT) & ZPCI_INDEX_MASK;

@@ -369,20 +371,36 @@ static void s390_domain_free(struct iommu_domain *domain)
 	call_rcu(&s390_domain->rcu, s390_iommu_rcu_free_domain);
 }
 
-static void s390_iommu_detach_device(struct iommu_domain *domain,
-				     struct device *dev)
+static void zdev_s390_domain_update(struct zpci_dev *zdev,
+				    struct iommu_domain *domain)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&zdev->dom_lock, flags);
+	zdev->s390_domain = domain;
+	spin_unlock_irqrestore(&zdev->dom_lock, flags);
+}
+
+static int blocking_domain_attach_device(struct iommu_domain *domain,
+					 struct device *dev)
 {
-	struct s390_domain *s390_domain = to_s390_domain(domain);
 	struct zpci_dev *zdev = to_zpci_dev(dev);
+	struct s390_domain *s390_domain;
 	unsigned long flags;
 
+	if (zdev->s390_domain->type == IOMMU_DOMAIN_BLOCKED)
+		return 0;
+
+	s390_domain = to_s390_domain(zdev->s390_domain);
 	spin_lock_irqsave(&s390_domain->list_lock, flags);

arch/s390/include/asm/pci.h +3 -8

 static int s390_iommu_attach_device(struct iommu_domain *domain,

@@ -401,20 +419,15 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
 		domain->geometry.aperture_end < zdev->start_dma))
 		return -EINVAL;
 
-	if (zdev->s390_domain)
-		s390_iommu_detach_device(&zdev->s390_domain->domain, dev);
+	blocking_domain_attach_device(&blocking_domain, dev);
 
+	/* If we fail now DMA remains blocked via blocking domain */
 	cc = zpci_register_ioat(zdev, 0, zdev->start_dma, zdev->end_dma,
 				virt_to_phys(s390_domain->dma_table), &status);
-	/*
-	 * If the device is undergoing error recovery the reset code
-	 * will re-establish the new domain.
-	 */
 	if (cc && status != ZPCI_PCI_ST_FUNC_NOT_AVAIL)
 		return -EIO;
-
 	zdev->dma_table = s390_domain->dma_table;
-	zdev->s390_domain = s390_domain;
+	zdev_s390_domain_update(zdev, domain);
 
 	spin_lock_irqsave(&s390_domain->list_lock, flags);
 	list_add_rcu(&zdev->iommu_list, &s390_domain->devices);

arch/s390/include/asm/pci.h +16 -12

-static void s390_iommu_release_device(struct device *dev)
-{
-	struct zpci_dev *zdev = to_zpci_dev(dev);
-
-	/*
-	 * release_device is expected to detach any domain currently attached
-	 * to the device, but keep it attached to other devices in the group.
-	 */
-	if (zdev)
-		s390_iommu_detach_device(&zdev->s390_domain->domain, dev);
+	return &zdev->iommu_dev;
 }
 
 static int zpci_refresh_all(struct zpci_dev *zdev)

@@ -697,9 +702,15 @@ static size_t s390_iommu_unmap_pages(struct iommu_domain *domain,
 
 struct zpci_iommu_ctrs *zpci_get_iommu_ctrs(struct zpci_dev *zdev)
 {
-	if (!zdev || !zdev->s390_domain)
+	struct s390_domain *s390_domain;
+
+	lockdep_assert_held(&zdev->dom_lock);
+
+	if (zdev->s390_domain->type == IOMMU_DOMAIN_BLOCKED)
 		return NULL;
-	return &zdev->s390_domain->ctrs;
+
+	s390_domain = to_s390_domain(zdev->s390_domain);
+	return &s390_domain->ctrs;
 }
 
 int zpci_init_iommu(struct zpci_dev *zdev)

@@ -776,11 +787,19 @@ static int __init s390_iommu_init(void)
 }
 subsys_initcall(s390_iommu_init);
 
+static struct iommu_domain blocking_domain = {
+	.type = IOMMU_DOMAIN_BLOCKED,
+	.ops = &(const struct iommu_domain_ops) {
+		.attach_dev	= blocking_domain_attach_device,
+	}
+};
+

This fixes a crash when surprise hot-unplugging a PCI device. This crash happens because during hot-unplug __iommu_group_set_domain_nofail() attaching the default domain fails when the platform no longer recognizes the device as it has already been removed and we end up with a NULL domain pointer and UAF. This is exactly the case referred to in the second comment in __iommu_device_set_domain() and just as stated there if we can instead attach the blocking domain the UAF is prevented as this can handle the already removed device. Implement the blocking domain to use this handling. With this change, the crash is fixed but we still hit a warning attempting to change DMA ownership on a blocked device.

Fixes c76c067e488c ("s390/pci: Use dma-iommu layer")

Co-developed-by Niklas Schnelle <[email protected]>

Signed-off-by Niklas Schnelle <[email protected]>

Signed-off-by Matthew Rosato <[email protected]>

---
Changes for v4:
- fix lockdep assert
Changes for v3:
- make blocking_domain type iommu_domain
- change zdev->s390_domain to type iommu_domain and remove most uses
- remove s390_iommu_detach_device, use blocking domain attach
- add spinlock to serialize zdev->s390_domain change / access to counters

---
 arch/s390/include/asm/pci.h |  4 +-
 arch/s390/pci/pci.c         |  3 ++
 arch/s390/pci/pci_debug.c   | 10 ++++-
 drivers/iommu/s390-iommu.c  | 73 +++++++++++++++++++++++--------------
 4 files changed, 59 insertions(+), 31 deletions(-)

This fixes a crash when surprise hot-unplugging a PCI device. This crash happens because during hot-unplug __iommu_group_set_domain_nofail() attaching the default domain fails when the platform no longer recognizes the device as it has already been removed and we end up with a NULL domain pointer and UAF. This is exactly the case referred to in the second comment in __iommu_device_set_domain() and just as stated there if we can instead attach the blocking domain the UAF is prevented as this can handle the already removed device. Implement the blocking domain to use this handling. With this change, the crash is fixed but we still hit a warning attempting to change DMA ownership on a blocked device.