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(-)
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;
+
+ /* 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
