From: Nicolin Chen <nicoleotsuka@gmail.com>
To: tony.luck@intel.com, fenghua.yu@intel.com
Cc: hch@lst.de, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [RFT][PATCH 3/7] ia64/sba_iommu: Avoid overflow at boundary_size
Date: Thu, 20 Aug 2020 16:20:18 -0700 [thread overview]
Message-ID: <20200820232018.23803-1-nicoleotsuka@gmail.com> (raw)
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/ia64/hp/common/sba_iommu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/ia64/hp/common/sba_iommu.c b/arch/ia64/hp/common/sba_iommu.c
index 656a4888c300..945954903bb0 100644
--- a/arch/ia64/hp/common/sba_iommu.c
+++ b/arch/ia64/hp/common/sba_iommu.c
@@ -485,8 +485,8 @@ sba_search_bitmap(struct ioc *ioc, struct device *dev,
ASSERT(((unsigned long) ioc->res_hint & (sizeof(unsigned long) - 1UL)) == 0);
ASSERT(res_ptr < res_end);
- boundary_size = (unsigned long long)dma_get_seg_boundary(dev) + 1;
- boundary_size = ALIGN(boundary_size, 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;
BUG_ON(ioc->ibase & ~iovp_mask);
shift = ioc->ibase >> iovp_shift;
--
2.17.1
reply other threads:[~2020-08-20 23:20 UTC|newest]
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