arm64: dma-mapping: always clear allocated buffers

mszyprow · wildea01 · commit 6829e274a623 · 2015-04-27T11:39:50.000+01:00
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: &lt;stable@vger.kernel.org&gt; # v3.14+
Signed-off-by: Marek Szyprowski &lt;m.szyprowski@samsung.com&gt;
Signed-off-by: Will Deacon &lt;will.deacon@arm.com&gt;
diff --git 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);
