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[SRU,F,3/3] s390/pci: fix zpci_zdev_put() on reserve

Message ID 20211103135637.2220305-4-frank.heimes@canonical.com
State New
Headers show
Series Reassign I/O Path of ConnectX-5 Port 1 before Port 2 causes NULL dereference (LP: 1943464) | expand

Commit Message

Frank Heimes Nov. 3, 2021, 1:56 p.m. UTC 
From: Niklas Schnelle <schnelle@linux.ibm.com>

BugLink: https://bugs.launchpad.net/bugs/1943464

Since commit 2a671f77ee49 ("s390/pci: fix use after free of zpci_dev")
the reference count of a zpci_dev is incremented between
pcibios_add_device() and pcibios_release_device() which was supposed to
prevent the zpci_dev from being freed while the common PCI code has
access to it. It was missed however that the handling of zPCI
availability events assumed that once zpci_zdev_put() was called no
later availability event would still see the device. With the previously
mentioned commit however this assumption no longer holds and we must
make sure that we only drop the initial long-lived reference the zPCI
subsystem holds exactly once.

Do so by introducing a zpci_device_reserved() function that handles when
a device is reserved. Here we make sure the zpci_dev will not be
considered for further events by removing it from the zpci_list.

This also means that the device actually stays in the
ZPCI_FN_STATE_RESERVED state between the time we know it has been
reserved and the final reference going away. We thus need to consider it
a real state instead of just a conceptual state after the removal. The
final cleanup of PCI resources, removal from zbus, and destruction of
the IOMMU stays in zpci_release_device() to make sure holders of the
reference do see valid data until the release.

Fixes: 2a671f77ee49 ("s390/pci: fix use after free of zpci_dev")
Cc: stable@vger.kernel.org
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
(backported from commit a46044a92add6a400f4dada7b943b30221f7cc80)
Signed-off-by: Frank Heimes <frank.heimes@canonical.com>
---
 arch/s390/include/asm/pci.h        |  3 ++
 arch/s390/pci/pci.c                | 45 ++++++++++++++++++++++++++----
 arch/s390/pci/pci_event.c          |  4 +--
 drivers/pci/hotplug/s390_pci_hpc.c |  9 +-----
 4 files changed, 46 insertions(+), 15 deletions(-)
diff mbox series

Patch

diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
index 5bcac3ac872d..74177c11611a 100644
--- a/arch/s390/include/asm/pci.h
+++ b/arch/s390/include/asm/pci.h
@@ -205,6 +205,9 @@  int zpci_create_device(struct zpci_dev *zdev);
 void zpci_remove_device(struct zpci_dev *zdev, bool set_error);
 int zpci_enable_device(struct zpci_dev *);
 int zpci_disable_device(struct zpci_dev *);
+void zpci_device_reserved(struct zpci_dev *zdev);
+bool zpci_is_device_configured(struct zpci_dev *zdev);
+
 int zpci_register_ioat(struct zpci_dev *, u8, u64, u64, u64);
 int zpci_unregister_ioat(struct zpci_dev *, u8);
 void zpci_remove_reserved_devices(void);
diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index 5e2fe6d682b7..563c9138d876 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -90,7 +90,7 @@  void zpci_remove_reserved_devices(void)
 	spin_unlock(&zpci_list_lock);
 
 	list_for_each_entry_safe(zdev, tmp, &remove, entry)
-		zpci_zdev_put(zdev);
+		zpci_device_reserved(zdev);
 }
 
 int pci_domain_nr(struct pci_bus *bus)
@@ -723,6 +723,14 @@  int zpci_disable_device(struct zpci_dev *zdev)
 }
 EXPORT_SYMBOL_GPL(zpci_disable_device);
 
+bool zpci_is_device_configured(struct zpci_dev *zdev)
+{
+	enum zpci_state state = zdev->state;
+
+	return state != ZPCI_FN_STATE_RESERVED &&
+		state != ZPCI_FN_STATE_STANDBY;
+}
+
 /* zpci_remove_device - Removes the given zdev from the PCI core
  * @zdev: the zdev to be removed from the PCI core
  * @set_error: if true the device's error state is set to permanent failure
@@ -796,6 +804,31 @@  int zpci_create_device(struct zpci_dev *zdev)
 	return rc;
 }
 
+/**
+ * zpci_device_reserved() - Mark device as resverved
+ * @zdev: the zpci_dev that was reserved
+ *
+ * Handle the case that a given zPCI function was reserved by another system.
+ * After a call to this function the zpci_dev can not be found via
+ * get_zdev_by_fid() anymore but may still be accessible via existing
+ * references though it will not be functional anymore.
+ */
+void zpci_device_reserved(struct zpci_dev *zdev)
+{
+	if (zdev->has_hp_slot)
+		zpci_exit_slot(zdev);
+	/*
+	 * Remove device from zpci_list as it is going away. This also
+	 * makes sure we ignore subsequent zPCI events for this device.
+	 */
+	spin_lock(&zpci_list_lock);
+	list_del(&zdev->entry);
+	spin_unlock(&zpci_list_lock);
+	zdev->state = ZPCI_FN_STATE_RESERVED;
+	zpci_dbg(3, "rsv fid:%x\n", zdev->fid);
+	zpci_zdev_put(zdev);
+}
+
 void zpci_release_device(struct kref *kref)
 {
 	struct zpci_dev *zdev = container_of(kref, struct zpci_dev, kref);
@@ -811,6 +844,12 @@  void zpci_release_device(struct kref *kref)
 	case ZPCI_FN_STATE_STANDBY:
 		if (zdev->has_hp_slot)
 			zpci_exit_slot(zdev);
+		spin_lock(&zpci_list_lock);
+		list_del(&zdev->entry);
+		spin_unlock(&zpci_list_lock);
+		zpci_dbg(3, "rsv fid:%x\n", zdev->fid);
+		fallthrough;
+	case ZPCI_FN_STATE_RESERVED:
 		zpci_cleanup_bus_resources(zdev);
 		zpci_bus_device_unregister(zdev);
 		zpci_destroy_iommu(zdev);
@@ -818,10 +857,6 @@  void zpci_release_device(struct kref *kref)
 	default:
 		break;
 	}
-
-	spin_lock(&zpci_list_lock);
-	list_del(&zdev->entry);
-	spin_unlock(&zpci_list_lock);
 	zpci_dbg(3, "rem fid:%x\n", zdev->fid);
 	kfree(zdev);
 }
diff --git a/arch/s390/pci/pci_event.c b/arch/s390/pci/pci_event.c
index c5b7980ff937..bdcf288cf8cc 100644
--- a/arch/s390/pci/pci_event.c
+++ b/arch/s390/pci/pci_event.c
@@ -146,7 +146,7 @@  static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf)
 		zdev->state = ZPCI_FN_STATE_STANDBY;
 		if (!clp_get_state(ccdf->fid, &state) &&
 		    state == ZPCI_FN_STATE_RESERVED) {
-			zpci_zdev_put(zdev);
+			zpci_device_reserved(zdev);
 		}
 		break;
 	case 0x0306: /* 0x308 or 0x302 for multiple devices */
@@ -155,7 +155,7 @@  static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf)
 	case 0x0308: /* Standby -> Reserved */
 		if (!zdev)
 			break;
-		zpci_zdev_put(zdev);
+		zpci_device_reserved(zdev);
 		break;
 	default:
 		break;
diff --git a/drivers/pci/hotplug/s390_pci_hpc.c b/drivers/pci/hotplug/s390_pci_hpc.c
index a047c421debe..93174f503464 100644
--- a/drivers/pci/hotplug/s390_pci_hpc.c
+++ b/drivers/pci/hotplug/s390_pci_hpc.c
@@ -109,14 +109,7 @@  static int get_power_status(struct hotplug_slot *hotplug_slot, u8 *value)
 	struct zpci_dev *zdev = container_of(hotplug_slot, struct zpci_dev,
 					     hotplug_slot);
 
-	switch (zdev->state) {
-	case ZPCI_FN_STATE_STANDBY:
-		*value = 0;
-		break;
-	default:
-		*value = 1;
-		break;
-	}
+	*value = zpci_is_device_configured(zdev) ? 1 : 0;
 	return 0;
 }