Nicolin Chen <nicoleotsuka@xxxxxxxxx> writes:
> 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.
>
> Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> Signed-off-by: Nicolin Chen <nicoleotsuka@xxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> ---
> arch/powerpc/kernel/iommu.c | 11 +++++------
> 1 file changed, 5 insertions(+), 6 deletions(-)
Are you asking for acks, or for maintainers to merge the patches
individually?
> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> index 9704f3f76e63..c01ccbf8afdd 100644
> --- a/arch/powerpc/kernel/iommu.c
> +++ b/arch/powerpc/kernel/iommu.c
> @@ -236,15 +236,14 @@ static unsigned long iommu_range_alloc(struct device *dev,
> }
> }
>
> - if (dev)
> - boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
> - 1 << tbl->it_page_shift);
> - else
> - boundary_size = ALIGN(1UL << 32, 1 << tbl->it_page_shift);
> /* 4GB boundary for iseries_hv_alloc and iseries_hv_map */
> + boundary_size = dev ? dma_get_seg_boundary(dev) : U32_MAX;
Is there any path that passes a NULL dev anymore?
Both iseries_hv_alloc() and iseries_hv_map() were removed years ago.
See:
8ee3e0d69623 ("powerpc: Remove the main legacy iSerie platform code")
So maybe we should do a lead-up patch that drops the NULL dev support,
which will then make this patch simpler.
cheers
> + /* Overflow-free shortcut for: ALIGN(b + 1, 1 << s) >> s */
> + boundary_size = (boundary_size >> tbl->it_page_shift) + 1;
>
> n = iommu_area_alloc(tbl->it_map, limit, start, npages, tbl->it_offset,
> - boundary_size >> tbl->it_page_shift, align_mask);
> + boundary_size, align_mask);
> if (n == -1) {
> if (likely(pass == 0)) {
> /* First try the pool from the start */
> --
> 2.17.1
