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* [PATCH] dma-mapping: Use unsigned types for size checks
@ 2019-08-12 19:03 Isaac J. Manjarres
  0 siblings, 0 replies; only message in thread
From: Isaac J. Manjarres @ 2019-08-12 19:03 UTC (permalink / raw)
  To: hch, m.szyprowski, robin.murphy
  Cc: Isaac J. Manjarres, linux-kernel, stable, iommu, lmark, pratikp

Both the size parameter in the dma_alloc_from_[dev/global]_coherent()
functions and the size field in the dma_coherent_mem structure
are represented by a signed quantity, which makes it so that any
comparisons between these two quantities is a signed comparison.

When a reserved memory region is larger than or equal to 2GB in
size, this will cause the most significant bit to be set to 1,
thus, treating the size as a negative number in signed

This can result in allocation failures when an amount of
memory that is strictly less than 2 GB is requested from
this region. The allocation fails because the signed comparison
to prevent from allocating more memory than what is in the
region in __dma_alloc_from_coherent() evaluates to true since
the size of the region is treated as a negative number, but the
size of the request is treated as a positive number.

Thus, change the type of the size parameter in the allocation
functions to an unsigned type, and change the type of the
size field in the dma_coherent_mem structure to an unsigned type
as well, as it does not make sense for sizes to be represented
by signed quantities.

Fixes: ee7e5516be4f ("generic: per-device coherent dma allocator")
Signed-off-by: Isaac J. Manjarres <>
 include/linux/dma-mapping.h | 6 +++---
 kernel/dma/coherent.c       | 8 ++++----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index f7d1eea..06d446d 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -159,14 +159,14 @@ static inline int is_device_dma_capable(struct device *dev)
  * These three functions are only for dma allocator.
  * Don't use them in device drivers.
-int dma_alloc_from_dev_coherent(struct device *dev, ssize_t size,
+int dma_alloc_from_dev_coherent(struct device *dev, size_t size,
 				       dma_addr_t *dma_handle, void **ret);
 int dma_release_from_dev_coherent(struct device *dev, int order, void *vaddr);
 int dma_mmap_from_dev_coherent(struct device *dev, struct vm_area_struct *vma,
 			    void *cpu_addr, size_t size, int *ret);
-void *dma_alloc_from_global_coherent(ssize_t size, dma_addr_t *dma_handle);
+void *dma_alloc_from_global_coherent(size_t size, dma_addr_t *dma_handle);
 int dma_release_from_global_coherent(int order, void *vaddr);
 int dma_mmap_from_global_coherent(struct vm_area_struct *vma, void *cpu_addr,
 				  size_t size, int *ret);
@@ -176,7 +176,7 @@ int dma_mmap_from_global_coherent(struct vm_area_struct *vma, void *cpu_addr,
 #define dma_release_from_dev_coherent(dev, order, vaddr) (0)
 #define dma_mmap_from_dev_coherent(dev, vma, vaddr, order, ret) (0)
-static inline void *dma_alloc_from_global_coherent(ssize_t size,
+static inline void *dma_alloc_from_global_coherent(size_t size,
 						   dma_addr_t *dma_handle)
 	return NULL;
diff --git a/kernel/dma/coherent.c b/kernel/dma/coherent.c
index 29fd659..c671d5c 100644
--- a/kernel/dma/coherent.c
+++ b/kernel/dma/coherent.c
@@ -13,7 +13,7 @@ struct dma_coherent_mem {
 	void		*virt_base;
 	dma_addr_t	device_base;
 	unsigned long	pfn_base;
-	int		size;
+	unsigned long	size;
 	unsigned long	*bitmap;
 	spinlock_t	spinlock;
 	bool		use_dev_dma_pfn_offset;
@@ -136,7 +136,7 @@ void dma_release_declared_memory(struct device *dev)
 static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem,
-		ssize_t size, dma_addr_t *dma_handle)
+		size_t size, dma_addr_t *dma_handle)
 	int order = get_order(size);
 	unsigned long flags;
@@ -179,7 +179,7 @@ static void *__dma_alloc_from_coherent(struct dma_coherent_mem *mem,
  * Returns 0 if dma_alloc_coherent should continue with allocating from
  * generic memory areas, or !0 if dma_alloc_coherent should return @ret.
-int dma_alloc_from_dev_coherent(struct device *dev, ssize_t size,
+int dma_alloc_from_dev_coherent(struct device *dev, size_t size,
 		dma_addr_t *dma_handle, void **ret)
 	struct dma_coherent_mem *mem = dev_get_coherent_memory(dev);
@@ -191,7 +191,7 @@ int dma_alloc_from_dev_coherent(struct device *dev, ssize_t size,
 	return 1;
-void *dma_alloc_from_global_coherent(ssize_t size, dma_addr_t *dma_handle)
+void *dma_alloc_from_global_coherent(size_t size, dma_addr_t *dma_handle)
 	if (!dma_coherent_default_memory)
 		return NULL;
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2019-08-12 19:03 [PATCH] dma-mapping: Use unsigned types for size checks Isaac J. Manjarres

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