Re: [PATCH v9 Kernel 4/5] vfio iommu: Implementation of ioctl to get dirty pages bitmap.

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 12 Nov 2019 22:33:39 +0530
Kirti Wankhede <kwankhede@nvidia.com> wrote:

> IOMMU container maintains list of external pinned pages. Bitmap of pinned
> pages for input IO virtual address range is created and returned.
> IO virtual address range should be from a single mapping created by
> map request. Input bitmap_size is validated by calculating the size of
> requested range.
> This ioctl returns bitmap of dirty pages, its user space application
> responsibility to copy content of dirty pages from source to destination
> during migration.
> 
> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> Reviewed-by: Neo Jia <cjia@nvidia.com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 92 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 92 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 2ada8e6cdb88..ac176e672857 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -850,6 +850,81 @@ static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu)
>  	return bitmap;
>  }
>  
> +/*
> + * start_iova is the reference from where bitmaping started. This is called
> + * from DMA_UNMAP where start_iova can be different than iova

Why not simply call this with a pointer to the bitmap relative to the
start of the iova?

> + */
> +
> +static int vfio_iova_dirty_bitmap(struct vfio_iommu *iommu, dma_addr_t iova,
> +				  size_t size, dma_addr_t start_iova,
> +				  unsigned long *bitmap)
> +{
> +	struct vfio_dma *dma;
> +	dma_addr_t temp_iova = iova;
> +
> +	dma = vfio_find_dma(iommu, iova, size);
> +	if (!dma)

The UAPI did not define that the user can only ask for the dirty bitmap
across a mapped range.

> +		return -EINVAL;
> +
> +	/*
> +	 * Range should be from a single mapping created by map request.
> +	 */

The UAPI also did not specify this as a requirement.

> +
> +	if ((iova < dma->iova) ||
> +	    ((dma->iova + dma->size) < (iova + size)))
> +		return -EINVAL;

Nor this.

So the actual implemented UAPI is that the user must call this over
some portion of, but not exceeding a single previously mapped DMA
range.  Why so restrictive?

> +
> +	while (temp_iova < iova + size) {
> +		struct vfio_pfn *vpfn = NULL;
> +
> +		vpfn = vfio_find_vpfn(dma, temp_iova);
> +		if (vpfn)
> +			__bitmap_set(bitmap, vpfn->iova - start_iova, 1);
> +
> +		temp_iova += PAGE_SIZE;

Seems like waking the rb tree would be far more efficient.  Also, if
dma->iommu_mapped, mark all pages dirty until we figure out how to
avoid it.

> +	}
> +
> +	return 0;
> +}
> +
> +static int verify_bitmap_size(unsigned long npages, unsigned long bitmap_size)
> +{
> +	unsigned long bsize = ALIGN(npages, BITS_PER_LONG) / 8;
> +
> +	if ((bitmap_size == 0) || (bitmap_size < bsize))
> +		return -EINVAL;
> +	return 0;
> +}
> +
> +static int vfio_iova_get_dirty_bitmap(struct vfio_iommu *iommu,
> +				struct vfio_iommu_type1_dirty_bitmap *range)
> +{
> +	unsigned long *bitmap;
> +	int ret;
> +
> +	ret = verify_bitmap_size(range->size >> PAGE_SHIFT, range->bitmap_size);
> +	if (ret)
> +		return ret;
> +
> +	/* one bit per page */
> +	bitmap = bitmap_zalloc(range->size >> PAGE_SHIFT, GFP_KERNEL);

This creates a DoS vector, we need to be able to directly use the user
bitmap or chunk words into it using a confined size (ex. a user can
with args 0 to UIN64_MAX). Thanks,

Alex

> +	if (!bitmap)
> +		return -ENOMEM;
> +
> +	mutex_lock(&iommu->lock);
> +	ret = vfio_iova_dirty_bitmap(iommu, range->iova, range->size,
> +				     range->iova, bitmap);
> +	mutex_unlock(&iommu->lock);
> +
> +	if (!ret) {
> +		if (copy_to_user(range->bitmap, bitmap, range->bitmap_size))
> +			ret = -EFAULT;
> +	}
> +
> +	bitmap_free(bitmap);
> +	return ret;
> +}
> +
>  static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>  			     struct vfio_iommu_type1_dma_unmap *unmap)
>  {
> @@ -2297,6 +2372,23 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
>  
>  		return copy_to_user((void __user *)arg, &unmap, minsz) ?
>  			-EFAULT : 0;
> +	} else if (cmd == VFIO_IOMMU_GET_DIRTY_BITMAP) {
> +		struct vfio_iommu_type1_dirty_bitmap range;
> +
> +		/* Supported for v2 version only */
> +		if (!iommu->v2)
> +			return -EACCES;
> +
> +		minsz = offsetofend(struct vfio_iommu_type1_dirty_bitmap,
> +					bitmap);
> +
> +		if (copy_from_user(&range, (void __user *)arg, minsz))
> +			return -EFAULT;
> +
> +		if (range.argsz < minsz)
> +			return -EINVAL;
> +
> +		return vfio_iova_get_dirty_bitmap(iommu, &range);
>  	}
>  
>  	return -ENOTTY;