Subject: Re: [RFC PATCH] vhost-vdpa: mark vhost device invalid to reflect vdpa device unregistration

From: "Michael S. Tsirkin" <[email-masked]>
Date: Sun, 4 Jul 2021 17:50:14 -0400

On Mon, Jul 05, 2021 at 02:22:04AM +0530, [email-masked] wrote:
> From: Gautam Dawar <[email-masked]>
> 
> As mentioned in Bug 213179, any malicious user-space application can render
> a module registering a vDPA device to hang forever. This will typically
> surface when vdpa_device_unregister() is called from the function
> responsible for module unload, leading rmmod commands to not return.
> 
> This patch unblocks the caller module by continuing with the clean-up
> but after marking the vhost device as unavailable. For future requests
> from user-space application, the vhost device availability is checked
> first and if it has gone unavailable, such requests are denied.
> 
> Signed-off-by: Gautam Dawar <[email-masked]>

I don't seem mappings handled below. Did I miss it?

> ---
>  drivers/vhost/vdpa.c | 45 ++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 39 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index e4b7d26649d8..623bc7f0c0ca 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -47,6 +47,7 @@ struct vhost_vdpa {
>  	int minor;
>  	struct eventfd_ctx *config_ctx;
>  	int in_batch;
> +	int dev_invalid;
>  	struct vdpa_iova_range range;
>  };
>  
> @@ -61,6 +62,11 @@ static void handle_vq_kick(struct vhost_work *work)
>  	struct vhost_vdpa *v = container_of(vq->dev, struct vhost_vdpa, vdev);
>  	const struct vdpa_config_ops *ops = v->vdpa->config;
>  
> +	if (v->dev_invalid) {
> +		dev_info(&v->dev,
> +			 "%s: vhost_vdpa device unavailable\n", __func__);
> +		return;
> +	}
>  	ops->kick_vq(v->vdpa, vq - v->vqs);
>  }
>  
> @@ -120,6 +126,11 @@ static void vhost_vdpa_reset(struct vhost_vdpa *v)
>  {
>  	struct vdpa_device *vdpa = v->vdpa;
>  
> +	if (v->dev_invalid) {
> +		dev_info(&v->dev,
> +			 "%s: vhost_vdpa device unavailable\n", __func__);
> +		return;
> +	}
>  	vdpa_reset(vdpa);
>  	v->in_batch = 0;
>  }
> @@ -367,6 +378,11 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
>  	u32 idx;
>  	long r;
>  
> +	if (v->dev_invalid) {
> +		dev_info(&v->dev,
> +			 "%s: vhost_vdpa device unavailable\n", __func__);
> +		return -ENODEV;
> +	}
>  	r = get_user(idx, (u32 __user *)argp);
>  	if (r < 0)
>  		return r;
> @@ -450,6 +466,11 @@ static long vhost_vdpa_unlocked_ioctl(struct file *filep,
>  		return 0;
>  	}
>  
> +	if (v->dev_invalid) {
> +		dev_info(&v->dev,
> +			 "%s: vhost_vdpa device unavailable\n", __func__);
> +		return -ENODEV;
> +	}
>  	mutex_lock(&d->mutex);
>  
>  	switch (cmd) {
> @@ -745,8 +766,13 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev *dev,
>  	const struct vdpa_config_ops *ops = vdpa->config;
>  	int r = 0;
>  
> -	mutex_lock(&dev->mutex);
> +	if (v->dev_invalid) {
> +		dev_info(&v->dev,
> +			 "%s: vhost_vdpa device unavailable\n", __func__);
> +		return -ENODEV;
> +	}
>  
> +	mutex_lock(&dev->mutex);
>  	r = vhost_dev_check_owner(dev);
>  	if (r)
>  		goto unlock;
> @@ -949,6 +975,11 @@ static vm_fault_t vhost_vdpa_fault(struct vm_fault *vmf)
>  	struct vm_area_struct *vma = vmf->vma;
>  	u16 index = vma->vm_pgoff;
>  
> +	if (v->dev_invalid) {
> +		dev_info(&v->dev,
> +			 "%s: vhost_vdpa device unavailable\n", __func__);
> +		return VM_FAULT_NOPAGE;
> +	}
>  	notify = ops->get_vq_notification(vdpa, index);
>  
>  	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> @@ -1091,11 +1122,13 @@ static void vhost_vdpa_remove(struct vdpa_device *vdpa)
>  		opened = atomic_cmpxchg(&v->opened, 0, 1);
>  		if (!opened)
>  			break;
> -		wait_for_completion_timeout(&v->completion,
> -					    msecs_to_jiffies(1000));
> -		dev_warn_once(&v->dev,
> -			      "%s waiting for /dev/%s to be closed\n",
> -			      __func__, dev_name(&v->dev));
> +		if (!wait_for_completion_timeout(&v->completion,
> +					    msecs_to_jiffies(1000))) {
> +			dev_warn(&v->dev,
> +				 "%s /dev/%s in use, continue..\n",
> +				 __func__, dev_name(&v->dev));
> +			break;
> +		}

When you have an arbitrary timeout you know something's not entirely
robust ...

>  	} while (1);
>  	put_device(&v->dev);
> +	v->dev_invalid = true;
> -- 
> 2.30.1