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

[Alex Williamson]

On Tue, 12 Nov 2019 22:33:39 +0530
Kirti Wankhede <address@hidden> 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 <address@hidden>
> Reviewed-by: Neo Jia <address@hidden>
> ---
>  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;