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SubjectRe: [PATCH 02/21] arm64/iommu: improve mmap bounds checking
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On 27/03/2019 08:04, Christoph Hellwig wrote:
> The nr_pages checks should be done for all mmap requests, not just those
> using remap_pfn_range.

Hmm, the logic in iommu_dma_mmap() inherently returns an error for the
"off >= nr_pages" case already. It's also supposed to be robust against
the "vma_pages(vma) > nr_pages - off" condition, although by making the
partial mapping and treating it as a success, rather than doing nothing
and returning an error. What's the exact motivation here?

Robin.

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> arch/arm64/mm/dma-mapping.c | 21 ++++++++-------------
> 1 file changed, 8 insertions(+), 13 deletions(-)
>
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index be88beb2e377..e54288921e72 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -73,19 +73,9 @@ static int __swiotlb_get_sgtable_page(struct sg_table *sgt,
> static int __swiotlb_mmap_pfn(struct vm_area_struct *vma,
> unsigned long pfn, size_t size)
> {
> - int ret = -ENXIO;
> - unsigned long nr_vma_pages = vma_pages(vma);
> - unsigned long nr_pages = PAGE_ALIGN(size) >> PAGE_SHIFT;
> - unsigned long off = vma->vm_pgoff;
> -
> - if (off < nr_pages && nr_vma_pages <= (nr_pages - off)) {
> - ret = remap_pfn_range(vma, vma->vm_start,
> - pfn + off,
> - vma->vm_end - vma->vm_start,
> - vma->vm_page_prot);
> - }
> -
> - return ret;
> + return remap_pfn_range(vma, vma->vm_start, pfn + vma->vm_pgoff,
> + vma->vm_end - vma->vm_start,
> + vma->vm_page_prot);
> }
> #endif /* CONFIG_IOMMU_DMA */
>
> @@ -241,6 +231,8 @@ static int __iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
> void *cpu_addr, dma_addr_t dma_addr, size_t size,
> unsigned long attrs)
> {
> + unsigned long nr_pages = PAGE_ALIGN(size) >> PAGE_SHIFT;
> + unsigned long off = vma->vm_pgoff;
> struct vm_struct *area;
> int ret;
>
> @@ -249,6 +241,9 @@ static int __iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
> if (dma_mmap_from_dev_coherent(dev, vma, cpu_addr, size, &ret))
> return ret;
>
> + if (off >= nr_pages || vma_pages(vma) > nr_pages - off)
> + return -ENXIO;
> +
> if (!is_vmalloc_addr(cpu_addr)) {
> unsigned long pfn = page_to_pfn(virt_to_page(cpu_addr));
> return __swiotlb_mmap_pfn(vma, pfn, size);
>

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