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

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Date:   Mon, 10 Dec 2018 16:31:45 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>, joro@...tes.org,
        Linux-MM <linux-mm@...ck.org>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 6/9] iommu/dma-iommu.c: Convert to use vm_insert_range

On 07/12/2018 20:41, Souptick Joarder wrote:
> On Fri, Dec 7, 2018 at 7:17 PM Robin Murphy <robin.murphy@....com> 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@...il.com>
>>> Reviewed-by: Matthew Wilcox <willy@...radead.org>
>>> ---
>>>    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.