Re: [PATCH 5/6] vduse: Support registering userspace memory for IOTLB

From: Yongji Xie
Date: Wed Jun 29 2022 - 05:26:20 EST

On Wed, Jun 29, 2022 at 4:43 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Wed, Jun 29, 2022 at 04:25:40PM +0800, Xie Yongji wrote:
> > Introduce two ioctls: VDUSE_IOTLB_REG_UMEM and
> > VDUSE_IOTLB_DEREG_UMEM to support registering
> > and de-registering userspace memory for IOTLB
> > in virtio-vdpa case.
> >
> > Now it only supports registering userspace memory
> > for IOTLB as bounce buffer.
> >
> > Signed-off-by: Xie Yongji <xieyongji@xxxxxxxxxxxxx>
> > ---
> > drivers/vdpa/vdpa_user/vduse_dev.c | 138 +++++++++++++++++++++++++++++
> > include/uapi/linux/vduse.h | 28 ++++++
> > 2 files changed, 166 insertions(+)
> >
> > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > index c47a5d9765cf..7b2ea7612da9 100644
> > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > @@ -21,6 +21,7 @@
> > #include <linux/uio.h>
> > #include <linux/vdpa.h>
> > #include <linux/nospec.h>
> > +#include <linux/sched/mm.h>
> > #include <uapi/linux/vduse.h>
> > #include <uapi/linux/vdpa.h>
> > #include <uapi/linux/virtio_config.h>
> > @@ -64,6 +65,13 @@ struct vduse_vdpa {
> > struct vduse_dev *dev;
> > };
> >
> > +struct vduse_iotlb_mem {
> > + unsigned long iova;
> > + unsigned long npages;
> > + struct page **pages;
> > + struct mm_struct *mm;
> > +};
> > +
> > struct vduse_dev {
> > struct vduse_vdpa *vdev;
> > struct device *dev;
> > @@ -95,6 +103,8 @@ struct vduse_dev {
> > u8 status;
> > u32 vq_num;
> > u32 vq_align;
> > + struct vduse_iotlb_mem *iotlb_mem;
> > + struct mutex mem_lock;
> > };
> >
> > struct vduse_dev_msg {
> > @@ -917,6 +927,100 @@ static int vduse_dev_queue_irq_work(struct vduse_dev *dev,
> > return ret;
> > }
> >
> > +static int vduse_dev_dereg_iotlb_mem(struct vduse_dev *dev,
> > + u64 iova, u64 size)
> > +{
> > + int ret;
> > +
> > + mutex_lock(&dev->mem_lock);
> > + ret = -ENOENT;
> > + if (!dev->iotlb_mem)
> > + goto unlock;
> > +
> > + ret = -EINVAL;
> > + if (dev->iotlb_mem->iova != iova || size != dev->domain->bounce_size)
> > + goto unlock;
> > +
> > + vduse_domain_remove_user_bounce_pages(dev->domain);
> > + unpin_user_pages(dev->iotlb_mem->pages, dev->iotlb_mem->npages);
>
> I notice you don't mark the pages dirty. This is going to be a problem.
>

Thanks for pointing out this, I will use unpin_user_pages_dirty_lock() instead.

> > + atomic64_sub(dev->iotlb_mem->npages, &dev->iotlb_mem->mm->pinned_vm);
> > + mmdrop(dev->iotlb_mem->mm);
> > + vfree(dev->iotlb_mem->pages);
> > + kfree(dev->iotlb_mem);
> > + dev->iotlb_mem = NULL;
> > + ret = 0;
> > +unlock:
> > + mutex_unlock(&dev->mem_lock);
> > + return ret;
> > +}
> > +
> > +static int vduse_dev_reg_iotlb_mem(struct vduse_dev *dev,
> > + u64 iova, u64 uaddr, u64 size)
> > +{
> > + struct page **page_list = NULL;
> > + struct vduse_iotlb_mem *mem = NULL;
> > + long pinned = 0;
> > + unsigned long npages, lock_limit;
> > + int ret;
> > +
> > + if (size != dev->domain->bounce_size ||
> > + iova != 0 || uaddr & ~PAGE_MASK)
> > + return -EINVAL;
> > +
> > + mutex_lock(&dev->mem_lock);
> > + ret = -EEXIST;
> > + if (dev->iotlb_mem)
> > + goto unlock;
> > +
> > + ret = -ENOMEM;
> > + npages = size >> PAGE_SHIFT;
> > + page_list = vmalloc(array_size(npages,
> > + sizeof(struct page *)));
>
> Is this basically trying to do a vmalloc with userspace-controlled size?
> That's an easy DOS vector.
>

We already checked the size before. The size must equal to (64MB >>
PAGE_SHIFT) now.

> > + mem = kzalloc(sizeof(*mem), GFP_KERNEL);
> > + if (!page_list || !mem)
> > + goto unlock;
> > +
> > + mmap_read_lock(current->mm);
> > +
> > + lock_limit = PFN_DOWN(rlimit(RLIMIT_MEMLOCK));
> > + if (npages + atomic64_read(&current->mm->pinned_vm) > lock_limit)
> > + goto out;
> > +
> > + pinned = pin_user_pages(uaddr, npages, FOLL_LONGTERM | FOLL_WRITE,
> > + page_list, NULL);
> > + if (pinned != npages) {
> > + ret = pinned < 0 ? pinned : -ENOMEM;
> > + goto out;
> > + }
>
>
> This is a popular approach but it's problematic if multiple
> devices try to pin the same page.

Do you mean the data would be corrupted if multiple devices use the
same page as bounce buffer? This is indeed a problem.

> Can this happen here?
>

I think we can't prevent this case now. I will do it in v2.

> > +
> > + ret = vduse_domain_add_user_bounce_pages(dev->domain,
> > + page_list, pinned);
> > + if (ret)
> > + goto out;
> > +
> > + atomic64_add(npages, &current->mm->pinned_vm);
> > +
> > + mem->pages = page_list;
> > + mem->npages = pinned;
> > + mem->iova = iova;
> > + mem->mm = current->mm;
> > + mmgrab(current->mm);
> > +
> > + dev->iotlb_mem = mem;
> > +out:
> > + if (ret && pinned > 0)
> > + unpin_user_pages(page_list, pinned);
> > +
> > + mmap_read_unlock(current->mm);
> > +unlock:
> > + if (ret) {
> > + vfree(page_list);
> > + kfree(mem);
> > + }
> > + mutex_unlock(&dev->mem_lock);
> > + return ret;
> > +}
> > +
> > static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
> > unsigned long arg)
> > {
> > @@ -943,6 +1047,16 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
> > if (entry.start > entry.last)
> > break;
> >
> > + if (domain->bounce_map && dev->iotlb_mem) {
> > + ret = -EEXIST;
> > + if (entry.start >= 0 &&
> > + entry.last < domain->bounce_size)
> > + break;
> > +
> > + if (entry.start < domain->bounce_size)
> > + entry.start = domain->bounce_size;
> > + }
> > +
> > spin_lock(&domain->iotlb_lock);
> > map = vhost_iotlb_itree_first(domain->iotlb,
> > entry.start, entry.last);
> > @@ -1102,6 +1216,28 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
> > ret = 0;
> > break;
> > }
> > + case VDUSE_IOTLB_REG_UMEM: {
> > + struct vduse_iotlb_umem umem;
> > +
> > + ret = -EFAULT;
> > + if (copy_from_user(&umem, argp, sizeof(umem)))
> > + break;
> > +
> > + ret = vduse_dev_reg_iotlb_mem(dev, umem.iova,
> > + umem.uaddr, umem.size);
> > + break;
> > + }
> > + case VDUSE_IOTLB_DEREG_UMEM: {
> > + struct vduse_iotlb_umem umem;
> > +
> > + ret = -EFAULT;
> > + if (copy_from_user(&umem, argp, sizeof(umem)))
> > + break;
> > +
> > + ret = vduse_dev_dereg_iotlb_mem(dev, umem.iova,
> > + umem.size);
> > + break;
> > + }
> > default:
> > ret = -ENOIOCTLCMD;
> > break;
> > @@ -1114,6 +1250,7 @@ static int vduse_dev_release(struct inode *inode, struct file *file)
> > {
> > struct vduse_dev *dev = file->private_data;
> >
> > + vduse_dev_dereg_iotlb_mem(dev, 0, dev->domain->bounce_size);
> > spin_lock(&dev->msg_lock);
> > /* Make sure the inflight messages can processed after reconncection */
> > list_splice_init(&dev->recv_list, &dev->send_list);
> > @@ -1176,6 +1313,7 @@ static struct vduse_dev *vduse_dev_create(void)
> > return NULL;
> >
> > mutex_init(&dev->lock);
> > + mutex_init(&dev->mem_lock);
> > spin_lock_init(&dev->msg_lock);
> > INIT_LIST_HEAD(&dev->send_list);
> > INIT_LIST_HEAD(&dev->recv_list);
> > diff --git a/include/uapi/linux/vduse.h b/include/uapi/linux/vduse.h
> > index c201b7a77c2c..1b17391e228f 100644
> > --- a/include/uapi/linux/vduse.h
> > +++ b/include/uapi/linux/vduse.h
> > @@ -227,6 +227,34 @@ struct vduse_iotlb_info {
> > /* Get IOTLB information, e.g. bounce buffer size */
> > #define VDUSE_IOTLB_GET_INFO _IOR(VDUSE_BASE, 0x18, struct vduse_iotlb_info)
> >
> > +/**
> > + * struct vduse_iotlb_umem - userspace memory configuration
> > + * @uaddr: start address of userspace memory, it must be aligned to page size
> > + * @iova: IOVA of userspace memory, it must be equal to bounce iova returned
> > + * by VDUSE_IOTLB_GET_INFO now
> > + * @size: size of userspace memory, it must be equal to bounce size returned
> > + * by VDUSE_IOTLB_GET_INFO now
> > + * @reserved: for future use, needs to be initialized to zero
>
> You should check that it's 0 in that case, otherwise userspace
> will conveniently forget.
>

OK, I will fix it.

Thanks,
Yongji