[3.19.y-ckt stable] Patch "arm64: dma-mapping: always clear allocated buffers" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    arm64: dma-mapping: always clear allocated buffers

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt1.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 27ecfe468fea56a3a9c423e462672964c622affe Mon Sep 17 00:00:00 2001
From: Marek Szyprowski <m.szyprowski at samsung.com>
Date: Thu, 23 Apr 2015 12:46:16 +0100
Subject: arm64: dma-mapping: always clear allocated buffers

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>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/arm64/mm/dma-mapping.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index df34a70..6efbb52 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);
--
1.9.1