commit a46044a92add6a400f4dada7b943b30221f7cc80 upstream.

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 Link: https://lore.kernel.org/r/20211012093425.2247924-1-schnelle@linux.ibm.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 --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h index a75d94a9bcb2..1226971533fe 100644 --- a/arch/s390/include/asm/pci.h +++ b/arch/s390/include/asm/pci.h @@ -205,6 +205,9 @@ int zpci_create_device(u32 fid, u32 fh, enum zpci_state state); 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 f5ddbc625c1a..e14e4a3a647a 100644 --- a/arch/s390/pci/pci.c +++ b/arch/s390/pci/pci.c @@ -92,7 +92,7 @@ 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) @@ -787,6 +787,39 @@ int zpci_create_device(u32 fid, u32 fh, enum zpci_state state) return rc; }

+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_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); @@ -802,6 +835,12 @@ 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); @@ -809,10 +848,6 @@ 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 ac0c65cdd69d..b7cfde7e80a8 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 */ @@ -156,7 +156,7 @@ 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; }