swiotlb-xen: fix DMA_ATTR_NO_KERNEL_MAPPING on arm

swiotlb-xen uses very different ways to allocate coherent memory on x86
vs arm.  On the former it allocates memory from the page allocator, while
on the later it reuses the dma-direct allocator the handles the
complexities of non-coherent DMA on arm platforms.

Unfortunately the complexities of trying to deal with the two cases in
the swiotlb-xen.c code lead to a bug in the handling of
DMA_ATTR_NO_KERNEL_MAPPING on arm.  With the DMA_ATTR_NO_KERNEL_MAPPING
flag the coherent memory allocator does not actually allocate coherent
memory, but just a DMA handle for some memory that is DMA addressable
by the device, but which does not have to have a kernel mapping.  Thus
dereferencing the return value will lead to kernel crashed and memory
corruption.

Fix this by using the dma-direct allocator directly for arm, which works
perfectly fine because on arm swiotlb-xen is only used when the domain is
1:1 mapped, and then simplifying the remaining code to only cater for the
x86 case with DMA coherent device.

Reported-by: Rahul Singh <Rahul.Singh@arm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Rahul Singh <rahul.singh@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Tested-by: Rahul Singh <rahul.singh@arm.com>

1 files changed, 0 insertions, 6 deletions

diff --git a/include/xen/swiotlb-xen.h b/include/xen/swiotlb-xen.h
index 590ceb923f0c..808d17ad8d57 100644
--- a/include/xen/swiotlb-xen.h
+++ b/include/xen/swiotlb-xen.h
@@ -10,12 +10,6 @@ void xen_dma_sync_for_cpu(struct device *dev, dma_addr_t handle,
 void xen_dma_sync_for_device(struct device *dev, dma_addr_t handle,
 			     size_t size, enum dma_data_direction dir);
 
-#ifdef CONFIG_SWIOTLB_XEN
-int xen_swiotlb_fixup(void *buf, unsigned long nslabs);
-#else
-#define xen_swiotlb_fixup NULL
-#endif
-
 extern const struct dma_map_ops xen_swiotlb_dma_ops;
 
 #endif /* __LINUX_SWIOTLB_XEN_H */