From 82d93f580f0be56eb36964bc39e85dd3ca0530bc Mon Sep 17 00:00:00 2001 From: Yi Liu Date: Tue, 18 Jul 2023 06:55:32 -0700 Subject: [PATCH] vfio: Block device access via device fd until device is opened Allow the vfio_device file to be in a state where the device FD is opened but the device cannot be used by userspace (i.e. its .open_device() hasn't been called). This inbetween state is not used when the device FD is spawned from the group FD, however when we create the device FD directly by opening a cdev it will be opened in the blocked state. The reason for the inbetween state is that userspace only gets a FD but doesn't gain access permission until binding the FD to an iommufd. So in the blocked state, only the bind operation is allowed. Completing bind will allow user to further access the device. This is implemented by adding a flag in struct vfio_device_file to mark the blocked state and using a simple smp_load_acquire() to obtain the flag value and serialize all the device setup with the thread accessing this device. Following this lockless scheme, it can safely handle the device FD unbound->bound but it cannot handle bound->unbound. To allow this we'd need to add a lock on all the vfio ioctls which seems costly. So once device FD is bound, it remains bound until the FD is closed. Suggested-by: Jason Gunthorpe Reviewed-by: Kevin Tian Reviewed-by: Jason Gunthorpe Reviewed-by: Eric Auger Tested-by: Terrence Xu Tested-by: Nicolin Chen Tested-by: Matthew Rosato Tested-by: Yanting Jiang Tested-by: Shameer Kolothum Tested-by: Zhenzhong Duan Signed-off-by: Yi Liu Link: https://lore.kernel.org/r/20230718135551.6592-8-yi.l.liu@intel.com Signed-off-by: Alex Williamson --- drivers/vfio/group.c | 11 ++++++++++- drivers/vfio/vfio.h | 1 + drivers/vfio/vfio_main.c | 16 ++++++++++++++++ 3 files changed, 27 insertions(+), 1 deletion(-) diff --git a/drivers/vfio/group.c b/drivers/vfio/group.c index caf53716ddb2e..088dd34c89319 100644 --- a/drivers/vfio/group.c +++ b/drivers/vfio/group.c @@ -194,9 +194,18 @@ static int vfio_df_group_open(struct vfio_device_file *df) df->iommufd = device->group->iommufd; ret = vfio_df_open(df); - if (ret) + if (ret) { df->iommufd = NULL; + goto out_put_kvm; + } + + /* + * Paired with smp_load_acquire() in vfio_device_fops::ioctl/ + * read/write/mmap and vfio_file_has_device_access() + */ + smp_store_release(&df->access_granted, true); +out_put_kvm: if (device->open_count == 0) vfio_device_put_kvm(device); diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h index 2094f5a4ef045..4478a1e77a5ed 100644 --- a/drivers/vfio/vfio.h +++ b/drivers/vfio/vfio.h @@ -19,6 +19,7 @@ struct vfio_container; struct vfio_device_file { struct vfio_device *device; + u8 access_granted; spinlock_t kvm_ref_lock; /* protect kvm field */ struct kvm *kvm; struct iommufd_ctx *iommufd; /* protected by struct vfio_device_set::lock */ diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c index 825b1eeaebe20..c37fc14599d0e 100644 --- a/drivers/vfio/vfio_main.c +++ b/drivers/vfio/vfio_main.c @@ -1129,6 +1129,10 @@ static long vfio_device_fops_unl_ioctl(struct file *filep, struct vfio_device *device = df->device; int ret; + /* Paired with smp_store_release() following vfio_df_open() */ + if (!smp_load_acquire(&df->access_granted)) + return -EINVAL; + ret = vfio_device_pm_runtime_get(device); if (ret) return ret; @@ -1156,6 +1160,10 @@ static ssize_t vfio_device_fops_read(struct file *filep, char __user *buf, struct vfio_device_file *df = filep->private_data; struct vfio_device *device = df->device; + /* Paired with smp_store_release() following vfio_df_open() */ + if (!smp_load_acquire(&df->access_granted)) + return -EINVAL; + if (unlikely(!device->ops->read)) return -EINVAL; @@ -1169,6 +1177,10 @@ static ssize_t vfio_device_fops_write(struct file *filep, struct vfio_device_file *df = filep->private_data; struct vfio_device *device = df->device; + /* Paired with smp_store_release() following vfio_df_open() */ + if (!smp_load_acquire(&df->access_granted)) + return -EINVAL; + if (unlikely(!device->ops->write)) return -EINVAL; @@ -1180,6 +1192,10 @@ static int vfio_device_fops_mmap(struct file *filep, struct vm_area_struct *vma) struct vfio_device_file *df = filep->private_data; struct vfio_device *device = df->device; + /* Paired with smp_store_release() following vfio_df_open() */ + if (!smp_load_acquire(&df->access_granted)) + return -EINVAL; + if (unlikely(!device->ops->mmap)) return -EINVAL; -- 2.30.2