arm64: dma-mapping: always clear allocated buffers

[ Upstream commit 6829e274 ]

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.

Bug: 29795245
CRs-Fixed: 1041735
Change-Id: I74bf024e0f603ca8c0b05430dc2ee154d579cfb2
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>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Git-commit: a142e964
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[lmark@codeaurora.org: resolve merge conflicts]
Signed-off-by: Liam Mark <lmark@codeaurora.org>