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

[Robin Murphy]

On 07/12/2018 20:41, Souptick Joarder wrote:
> 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);

Yup, I think that looks appropriate.

Robin.