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    Subject[RESEND][PATCH 4/7] s390/pci_dma: Avoid overflow at boundary_size
    Date
    The boundary_size might be as large as ULONG_MAX, which means
    that a device has no specific boundary limit. So either "+ 1"
    or passing it to ALIGN() would potentially overflow.

    According to kernel defines:
    #define ALIGN_MASK(x, mask) (((x) + (mask)) & ~(mask))
    #define ALIGN(x, a) ALIGN_MASK(x, (typeof(x))(a) - 1)

    We can simplify the logic here:
    ALIGN(boundary + 1, 1 << shift) >> shift
    = ALIGN_MASK(b + 1, (1 << s) - 1) >> s
    = {[b + 1 + (1 << s) - 1] & ~[(1 << s) - 1]} >> s
    = [b + 1 + (1 << s) - 1] >> s
    = [b + (1 << s)] >> s
    = (b >> s) + 1

    So fixing a potential overflow with the safer shortcut.

    Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
    Cc: Christoph Hellwig <hch@lst.de>
    ---
    arch/s390/pci/pci_dma.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/arch/s390/pci/pci_dma.c b/arch/s390/pci/pci_dma.c
    index 64b1399a73f0..ecb067acc6d5 100644
    --- a/arch/s390/pci/pci_dma.c
    +++ b/arch/s390/pci/pci_dma.c
    @@ -263,8 +263,8 @@ static unsigned long __dma_alloc_iommu(struct device *dev,
    struct zpci_dev *zdev = to_zpci(to_pci_dev(dev));
    unsigned long boundary_size;

    - boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
    - PAGE_SIZE) >> PAGE_SHIFT;
    + /* Overflow-free shortcut for: ALIGN(b + 1, 1 << s) >> s */
    + boundary_size = (dma_get_seg_boundary(dev) >> PAGE_SHIFT) + 1;
    return iommu_area_alloc(zdev->iommu_bitmap, zdev->iommu_pages,
    start, size, zdev->start_dma >> PAGE_SHIFT,
    boundary_size, 0);
    --
    2.17.1
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