[RFC PATCH 30/30] vfio: Allow to bind foreign task

[Tomasz Nowicki]

On 27.02.2017 20:54, Jean-Philippe Brucker wrote:
> Let the process that owns the device create an address space bond on
> behalf of another process. We add a pid argument to the BIND_TASK ioctl,
> allowing the caller to bind a foreign task. The expected program flow in
> this case is:
>
> * Process A creates the VFIO context and initializes the device.
> * Process B asks A to bind its address space.
> * Process A issues an ioctl to the VFIO device fd with BIND_TASK(pid).
>   It may communicate the given PASID back to process B or keep track of it
>   internally.
> * Process B asks A to perform transactions on its virtual address.
> * Process A launches transaction tagged with the given PASID.
>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker at arm.com>
> ---
>  drivers/vfio/vfio.c       | 35 +++++++++++++++++++++++++++++++++--
>  include/uapi/linux/vfio.h | 15 +++++++++++++++
>  2 files changed, 48 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> index c4505d8f4c61..ecc5d07e3dbb 100644
> --- a/drivers/vfio/vfio.c
> +++ b/drivers/vfio/vfio.c
> @@ -26,6 +26,7 @@
>  #include <linux/module.h>
>  #include <linux/mutex.h>
>  #include <linux/pci.h>
> +#include <linux/ptrace.h>
>  #include <linux/rwsem.h>
>  #include <linux/sched.h>
>  #include <linux/slab.h>
> @@ -1660,7 +1661,7 @@ static long vfio_svm_ioctl(struct vfio_device *device, unsigned int cmd,
>  	struct vfio_device_svm svm;
>  	struct vfio_task *vfio_task;
>
> -	minsz = offsetofend(struct vfio_device_svm, pasid);
> +	minsz = offsetofend(struct vfio_device_svm, pid);
>
>  	if (copy_from_user(&svm, (void __user *)arg, minsz))
>  		return -EFAULT;
> @@ -1669,9 +1670,39 @@ static long vfio_svm_ioctl(struct vfio_device *device, unsigned int cmd,
>  		return -EINVAL;
>
>  	if (cmd == VFIO_DEVICE_BIND_TASK) {
> -		struct task_struct *task = current;
> +		struct mm_struct *mm;
> +		struct task_struct *task;
> +
> +		if (svm.flags & ~VFIO_SVM_PID)
> +			return -EINVAL;
> +
> +		if (svm.flags & VFIO_SVM_PID) {
> +			rcu_read_lock();
> +			task = find_task_by_vpid(svm.pid);
> +			if (task)
> +				get_task_struct(task);
> +			rcu_read_unlock();
> +			if (!task)
> +				return -ESRCH;
> +
> +			/*
> +			 * Ensure process has RW access on the task's mm
> +			 * FIXME:
> +			 * - I think this ought to be in the IOMMU API
> +			 * - I'm assuming permission is never revoked during the
> +			 *   task's lifetime. Might be mistaken.
> +			 */
> +			mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
> +			if (!mm || IS_ERR(mm))

I know this is RFC patch but considering we will keep this as is, we 
need here:
+put_task_struct(task);


> +				return IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
> +			mmput(mm);
> +		} else {
> +			get_task_struct(current);
> +			task = current;
> +		}
>
>  		ret = iommu_bind_task(device->dev, task, &svm.pasid, 0, NULL);
> +		put_task_struct(task);
>  		if (ret)
>  			return ret;
>

Thanks,
Tomasz