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@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
---
drivers/parisc/ccio-dma.c | 4 ++--
drivers/parisc/sba_iommu.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/parisc/ccio-dma.c b/drivers/parisc/ccio-dma.c
index a5507f75b524..c667d6aba764 100644
--- a/drivers/parisc/ccio-dma.c
+++ b/drivers/parisc/ccio-dma.c
@@ -356,8 +356,8 @@ ccio_alloc_range(struct ioc *ioc, struct device *dev, size_t size)
** ggg sacrifices another 710 to the computer gods.
*/
- boundary_size = ALIGN((unsigned long long)dma_get_seg_boundary(dev) + 1,
- 1ULL << IOVP_SHIFT) >> IOVP_SHIFT;
+ /* Overflow-free shortcut for: ALIGN(b + 1, 1 << s) >> s */
+ boundary_size = (dma_get_seg_boundary(dev) >> IOVP_SHIFT) + 1;
if (pages_needed <= 8) {
/*
diff --git a/drivers/parisc/sba_iommu.c b/drivers/parisc/sba_iommu.c
index d4314fba0269..96bc2c617cbd 100644
--- a/drivers/parisc/sba_iommu.c
+++ b/drivers/parisc/sba_iommu.c
@@ -342,8 +342,8 @@ sba_search_bitmap(struct ioc *ioc, struct device *dev,
unsigned long shift;
int ret;
- boundary_size = ALIGN((unsigned long long)dma_get_seg_boundary(dev) + 1,
- 1ULL << IOVP_SHIFT) >> IOVP_SHIFT;
+ /* Overflow-free shortcut for: ALIGN(b + 1, 1 << s) >> s */
+ boundary_size = (dma_get_seg_boundary(dev) >> IOVP_SHIFT) + 1;
#if defined(ZX1_SUPPORT)
BUG_ON(ioc->ibase & ~IOVP_MASK);
--
2.17.1
|