On Tue, Sep 01, 2020 at 11:27:36PM +1000, Michael Ellerman wrote:
> 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?
I was expecting that but Christoph just suggested me to squash them
into one so he would merge it: https://lkml.org/lkml/2020/9/1/159
Though I feel it'd be nice to get maintainers' acks before merging.
> > 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.
The next version of this change will follow Christoph's suggestion
by having a helper function that takes care of !dev internally.
Thanks
Nic
>
>
> > + /* 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
