arm64: dma-mapping: always clear allocated buffers

Buffers allocated by dma_alloc_coherent() are always zeroed on Alpha,
ARM (32bit), MIPS, PowerPC, x86/x86_64 and probably other architectures.
It turned out that some drivers rely on this 'feature'. Allocated buffer
might be also exposed to userspace with dma_mmap() call, so clearing it
is desired from security point of view to avoid exposing random memory
to userspace. This patch unifies dma_alloc_coherent() behavior on ARM64
architecture with other implementations by unconditionally zeroing
allocated buffer.

Cc: <stable@vger.kernel.org> # v3.14+
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 2 insertions, 4 deletions

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index ef7d112f5ce0..e0f14ee26b68 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -67,8 +67,7 @@ static void *__alloc_from_pool(size_t size, struct page **ret_page, gfp_t flags)
 
                 *ret_page = phys_to_page(phys);
                 ptr = (void *)val;
-                if (flags & __GFP_ZERO)
-                        memset(ptr, 0, size);
+                memset(ptr, 0, size);
         }
 
         return ptr;
@@ -113,8 +112,7 @@ static void *__dma_alloc_coherent(struct device *dev, size_t size,
 
                 *dma_handle = phys_to_dma(dev, page_to_phys(page));
                 addr = page_address(page);
-                if (flags & __GFP_ZERO)
-                        memset(addr, 0, size);
+                memset(addr, 0, size);
                 return addr;
         } else {
                 return swiotlb_alloc_coherent(dev, size, dma_handle, flags);