[RESEND][PATCH 5/7] sparc: Avoid overflow at boundary_size

From: Nicolin Chen
Date: Mon Aug 31 2020 - 16:39:18 EST


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>
---
arch/sparc/kernel/iommu-common.c | 9 +++------
arch/sparc/kernel/iommu.c | 4 ++--
arch/sparc/kernel/pci_sun4v.c | 4 ++--
3 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/arch/sparc/kernel/iommu-common.c b/arch/sparc/kernel/iommu-common.c
index 59cb16691322..843e71894d04 100644
--- a/arch/sparc/kernel/iommu-common.c
+++ b/arch/sparc/kernel/iommu-common.c
@@ -166,13 +166,10 @@ unsigned long iommu_tbl_range_alloc(struct device *dev,
}
}

- if (dev)
- boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
- 1 << iommu->table_shift);
- else
- boundary_size = ALIGN(1ULL << 32, 1 << iommu->table_shift);
+ boundary_size = dev ? dma_get_seg_boundary(dev) : U32_MAX;

- boundary_size = boundary_size >> iommu->table_shift;
+ /* Overflow-free shortcut for: ALIGN(b + 1, 1 << s) >> s */
+ boundary_size = (boundary_size >> iommu->table_shift) + 1;
/*
* if the skip_span_boundary_check had been set during init, we set
* things up so that iommu_is_span_boundary() merely checks if the
diff --git a/arch/sparc/kernel/iommu.c b/arch/sparc/kernel/iommu.c
index 4ae7388b1bff..d981c37305ae 100644
--- a/arch/sparc/kernel/iommu.c
+++ b/arch/sparc/kernel/iommu.c
@@ -472,8 +472,8 @@ static int dma_4u_map_sg(struct device *dev, struct scatterlist *sglist,
outs->dma_length = 0;

max_seg_size = dma_get_max_seg_size(dev);
- seg_boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
- IO_PAGE_SIZE) >> IO_PAGE_SHIFT;
+ /* Overflow-free shortcut for: ALIGN(b + 1, 1 << s) >> s */
+ seg_boundary_size = (dma_get_seg_boundary(dev) >> IO_PAGE_SHIFT) + 1;
base_shift = iommu->tbl.table_map_base >> IO_PAGE_SHIFT;
for_each_sg(sglist, s, nelems, i) {
unsigned long paddr, npages, entry, out_entry = 0, slen;
diff --git a/arch/sparc/kernel/pci_sun4v.c b/arch/sparc/kernel/pci_sun4v.c
index 14b93c5564e3..233fe8a20cec 100644
--- a/arch/sparc/kernel/pci_sun4v.c
+++ b/arch/sparc/kernel/pci_sun4v.c
@@ -508,8 +508,8 @@ static int dma_4v_map_sg(struct device *dev, struct scatterlist *sglist,
iommu_batch_start(dev, prot, ~0UL);

max_seg_size = dma_get_max_seg_size(dev);
- seg_boundary_size = ALIGN(dma_get_seg_boundary(dev) + 1,
- IO_PAGE_SIZE) >> IO_PAGE_SHIFT;
+ /* Overflow-free shortcut for: ALIGN(b + 1, 1 << s) >> s */
+ seg_boundary_size = (dma_get_seg_boundary(dev) >> IO_PAGE_SHIFT) + 1;

mask = *dev->dma_mask;
if (!iommu_use_atu(iommu, mask))
--
2.17.1