Re: [PATCH v3 6/9] iommu/dma-iommu.c: Convert to use vm_insert_range

[Souptick Joarder]

On Fri, Dec 7, 2018 at 7:17 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
>
> On 06/12/2018 18:43, Souptick Joarder wrote:
> > Convert to use vm_insert_range() to map range of kernel
> > memory to user vma.
> >
> > Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> > Reviewed-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/dma-iommu.c | 13 +++----------
> >   1 file changed, 3 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index d1b0475..a2c65e2 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -622,17 +622,10 @@ struct page **iommu_dma_alloc(struct device *dev, size_t size, gfp_t gfp,
> >
> >   int iommu_dma_mmap(struct page **pages, size_t size, struct vm_area_struct *vma)
> >   {
> > -     unsigned long uaddr = vma->vm_start;
> > -     unsigned int i, count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> > -     int ret = -ENXIO;
> > +     unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> >
> > -     for (i = vma->vm_pgoff; i < count && uaddr < vma->vm_end; i++) {
> > -             ret = vm_insert_page(vma, uaddr, pages[i]);
> > -             if (ret)
> > -                     break;
> > -             uaddr += PAGE_SIZE;
> > -     }
> > -     return ret;
> > +     return vm_insert_range(vma, vma->vm_start,
> > +                             pages + vma->vm_pgoff, count);
>
> You also need to adjust count to compensate for the pages skipped by
> vm_pgoff, otherwise you've got an out-of-bounds dereference triggered
> from userspace, which is pretty high up the "not good" scale (not to
> mention the entire call would then propagate -EFAULT back from
> vm_insert_page() and thus always appear to fail for nonzero offsets).

So this should something similar to ->

        return vm_insert_range(vma, vma->vm_start,
                                pages + vma->vm_pgoff, count - vma->vm_pgoff);