From: Parav Pandit parav@mellanox.com

mainline inclusion from mainline-5.2 commit 522ecce08ab20b57342d65b05601818e0f95fb2c category: bugfix bugzilla: NA CVE: NA

-------------------------------------------------

This patch addresses below two issues and prepares the code to address 3rd issue listed below.

1. mdev device is placed on the mdev bus before it is created in the vendor driver. Once a device is placed on the mdev bus without creating its supporting underlying vendor device, mdev driver's probe() gets triggered. However there isn't a stable mdev available to work on.

create_store() mdev_create_device() device_register() ... vfio_mdev_probe() [...] parent->ops->create() vfio_ap_mdev_create() mdev_set_drvdata(mdev, matrix_mdev); /* Valid pointer set above */

Due to this way of initialization, mdev driver who wants to use the mdev, doesn't have a valid mdev to work on.

2. Current creation sequence is, parent->ops_create() groups_register()

Remove sequence is, parent->ops->remove() groups_unregister()

However, remove sequence should be exact mirror of creation sequence. Once this is achieved, all users of the mdev will be terminated first before removing underlying vendor device. (Follow standard linux driver model). At that point vendor's remove() ops shouldn't fail because taking the device off the bus should terminate any usage.

3. When remove operation fails, mdev sysfs removal attempts to add the file back on already removed device. Following call trace [1] is observed.

[1] call trace: kernel: WARNING: CPU: 2 PID: 9348 at fs/sysfs/file.c:327 sysfs_create_file_ns+0x7f/0x90 kernel: CPU: 2 PID: 9348 Comm: bash Kdump: loaded Not tainted 5.1.0-rc6-vdevbus+ #6 kernel: Hardware name: Supermicro SYS-6028U-TR4+/X10DRU-i+, BIOS 2.0b 08/09/2016 kernel: RIP: 0010:sysfs_create_file_ns+0x7f/0x90 kernel: Call Trace: kernel: remove_store+0xdc/0x100 [mdev] kernel: kernfs_fop_write+0x113/0x1a0 kernel: vfs_write+0xad/0x1b0 kernel: ksys_write+0x5a/0xe0 kernel: do_syscall_64+0x5a/0x210 kernel: entry_SYSCALL_64_after_hwframe+0x49/0xbe

Therefore, mdev core is improved in following ways.

1. Split the device registration/deregistration sequence so that some things can be done between initialization of the device and hooking it up to the bus respectively after deregistering it from the bus but before giving up our final reference. In particular, this means invoking the ->create() and ->remove() callbacks in those new windows. This gives the vendor driver an initialized mdev device to work with during creation. At the same time, a bus driver who wish to bind to mdev driver also gets initialized mdev device.

This follows standard Linux kernel bus and device model.

2. During remove flow, first remove the device from the bus. This ensures that any bus specific devices are removed. Once device is taken off the mdev bus, invoke remove() of mdev from the vendor driver.

3. The driver core device model provides way to register and auto unregister the device sysfs attribute groups at dev->groups. Make use of dev->groups to let core create the groups and eliminate code to avoid explicit groups creation and removal.

To ensure, that new sequence is solid, a below stack dump of a process is taken who attempts to remove the device while device is in use by vfio driver and user application. This stack dump validates that vfio driver guards against such device removal when device is in use.

cat /proc/21962/stack [<0>] vfio_del_group_dev+0x216/0x3c0 [vfio] [<0>] mdev_remove+0x21/0x40 [mdev] [<0>] device_release_driver_internal+0xe8/0x1b0 [<0>] bus_remove_device+0xf9/0x170 [<0>] device_del+0x168/0x350 [<0>] mdev_device_remove_common+0x1d/0x50 [mdev] [<0>] mdev_device_remove+0x8c/0xd0 [mdev] [<0>] remove_store+0x71/0x90 [mdev] [<0>] kernfs_fop_write+0x113/0x1a0 [<0>] vfs_write+0xad/0x1b0 [<0>] ksys_write+0x5a/0xe0 [<0>] do_syscall_64+0x5a/0x210 [<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe [<0>] 0xffffffffffffffff

This prepares the code to eliminate calling device_create_file() in subsequent patch.

Reviewed-by: Cornelia Huck cohuck@redhat.com Signed-off-by: Parav Pandit parav@mellanox.com Signed-off-by: Alex Williamson alex.williamson@redhat.com

Conflicts: drivers/vfio/mdev/mdev_core.c -mdev_device_remove_ops() and -mdev_device_remove_cb() are removed anyway, although they are not identical compared within the original patch. The type of uuid is still uuid_le, and it has not been changed to guid_t. drivers/vfio/mdev/mdev_private.h The type of uuid is still uuid_le, and it has not been changed to guid_t.

Signed-off-by: Xiaoyang Xu xuxiaoyang2@huawei.com Reviewed-by: Yingtai Xie xieyingtai@huawei.com Reviewed-by: Hanjun Guo guohanjun@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- drivers/vfio/mdev/mdev_core.c | 94 +++++++++++----------------------------- drivers/vfio/mdev/mdev_private.h | 2 +- drivers/vfio/mdev/mdev_sysfs.c | 2 +- 3 files changed, 27 insertions(+), 71 deletions(-)

diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c index e052f62..9705a4a 100644 --- a/drivers/vfio/mdev/mdev_core.c +++ b/drivers/vfio/mdev/mdev_core.c @@ -103,55 +103,10 @@ static inline void mdev_put_parent(struct mdev_parent *parent) kref_put(&parent->ref, mdev_release_parent); }

-static int mdev_device_create_ops(struct kobject *kobj, - struct mdev_device *mdev) -{ - struct mdev_parent *parent = mdev->parent; - int ret; - - ret = parent->ops->create(kobj, mdev); - if (ret) - return ret; - - ret = sysfs_create_groups(&mdev->dev.kobj, - parent->ops->mdev_attr_groups); - if (ret) - parent->ops->remove(mdev); - - return ret; -} - -/* - * mdev_device_remove_ops gets called from sysfs's 'remove' and when parent - * device is being unregistered from mdev device framework. - * - 'force_remove' is set to 'false' when called from sysfs's 'remove' which - * indicates that if the mdev device is active, used by VMM or userspace - * application, vendor driver could return error then don't remove the device. - * - 'force_remove' is set to 'true' when called from mdev_unregister_device() - * which indicate that parent device is being removed from mdev device - * framework so remove mdev device forcefully. - */ -static int mdev_device_remove_ops(struct mdev_device *mdev, bool force_remove) -{ - struct mdev_parent *parent = mdev->parent; - int ret; - - /* - * Vendor driver can return error if VMM or userspace application is - * using this mdev device. - */ - ret = parent->ops->remove(mdev); - if (ret && !force_remove) - return -EBUSY; - - sysfs_remove_groups(&mdev->dev.kobj, parent->ops->mdev_attr_groups); - return 0; -} - static int mdev_device_remove_cb(struct device *dev, void *data) { if (dev_is_mdev(dev)) - mdev_device_remove(dev, true); + mdev_device_remove(dev);

return 0; } @@ -311,41 +266,43 @@ int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le uuid) mdev->parent = parent; kref_init(&mdev->ref);

+ device_initialize(&mdev->dev); mdev->dev.parent = dev; mdev->dev.bus = &mdev_bus_type; mdev->dev.release = mdev_device_release; dev_set_name(&mdev->dev, "%pUl", uuid.b); + mdev->dev.groups = parent->ops->mdev_attr_groups; + mdev->type_kobj = kobj;

- ret = device_register(&mdev->dev); - if (ret) { - put_device(&mdev->dev); - goto mdev_fail; - } + ret = parent->ops->create(kobj, mdev); + if (ret) + goto ops_create_fail;

- ret = mdev_device_create_ops(kobj, mdev); + ret = device_add(&mdev->dev); if (ret) - goto create_fail; + goto add_fail;

ret = mdev_create_sysfs_files(&mdev->dev, type); - if (ret) { - mdev_device_remove_ops(mdev, true); - goto create_fail; - } + if (ret) + goto sysfs_fail;

- mdev->type_kobj = kobj; mdev->active = true; dev_dbg(&mdev->dev, "MDEV: created\n");

return 0;

-create_fail: - device_unregister(&mdev->dev); +sysfs_fail: + device_del(&mdev->dev); +add_fail: + parent->ops->remove(mdev); +ops_create_fail: + put_device(&mdev->dev); mdev_fail: mdev_put_parent(parent); return ret; }

-int mdev_device_remove(struct device *dev, bool force_remove) +int mdev_device_remove(struct device *dev) { struct mdev_device *mdev, *tmp; struct mdev_parent *parent; @@ -374,16 +331,15 @@ int mdev_device_remove(struct device *dev, bool force_remove) mutex_unlock(&mdev_list_lock);

type = to_mdev_type(mdev->type_kobj); + mdev_remove_sysfs_files(dev, type); + device_del(&mdev->dev); parent = mdev->parent; + ret = parent->ops->remove(mdev); + if (ret) + dev_err(&mdev->dev, "Remove failed: err=%d\n", ret);

- ret = mdev_device_remove_ops(mdev, force_remove); - if (ret) { - mdev->active = true; - return ret; - } - - mdev_remove_sysfs_files(dev, type); - device_unregister(dev); + /* Balances with device_initialize() */ + put_device(&mdev->dev); mdev_put_parent(parent);

return 0; diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h index b5819b7..9c65d8e 100644 --- a/drivers/vfio/mdev/mdev_private.h +++ b/drivers/vfio/mdev/mdev_private.h @@ -59,6 +59,6 @@ struct mdev_type { void mdev_remove_sysfs_files(struct device *dev, struct mdev_type *type);

int mdev_device_create(struct kobject *kobj, struct device *dev, uuid_le uuid); -int mdev_device_remove(struct device *dev, bool force_remove); +int mdev_device_remove(struct device *dev);

#endif /* MDEV_PRIVATE_H */ diff --git a/drivers/vfio/mdev/mdev_sysfs.c b/drivers/vfio/mdev/mdev_sysfs.c index e7770b5..1286366 100644 --- a/drivers/vfio/mdev/mdev_sysfs.c +++ b/drivers/vfio/mdev/mdev_sysfs.c @@ -236,7 +236,7 @@ static ssize_t remove_store(struct device *dev, struct device_attribute *attr, if (val && device_remove_file_self(dev, attr)) { int ret;

- ret = mdev_device_remove(dev, false); + ret = mdev_device_remove(dev); if (ret) { device_create_file(dev, attr); return ret;