[PATCH 3.16.y-ckt 014/129] arm64: dma-mapping: always clear allocated buffers

[Luis Henriques]

3.16.7-ckt12 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Marek Szyprowski <m.szyprowski at samsung.com>

commit 6829e274a623187c24f7cfc0e3d35f25d087fcc5 upstream.

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.

Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
[ luis: backported to 3.16:
  - dropped changes to __alloc_from_pool() which doesn't exist in 3.16 ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/arm64/mm/dma-mapping.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index de3abbe6c59f..893802645efe 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -65,8 +65,7 @@ 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);