linux-kernel - [PATCH v2] ARM: dma-mapping: always clear allocated buffers

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Date:   Wed, 25 Jul 2018 15:07:06 +0800
From:   YueHaibing <yuehaibing@...wei.com>
To:     <linux@...linux.org.uk>, <matthias.bgg@...il.com>,
        <vladimir.murzin@....com>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <akpm@...ux-foundation.org>, <iamjoonsoo.kim@....com>,
        <robin.murphy@....com>, <treding@...dia.com>,
        <zhongjiang@...wei.com>, <sean.wang@...iatek.com>,
        YueHaibing <yuehaibing@...wei.com>
Subject: [PATCH v2] ARM: dma-mapping: always clear allocated buffers

Sean Wang reported dma_zalloc_coherent doesn't work as expect on his
armv7,the allocated mem is not zeroed.The reason is __alloc_from_pool
doesn't honor __GFP_ZERO.

As commit 6829e274a623 ("arm64: dma-mapping: always clear allocated buffers")
has pointed out,buffers allocated by dma_alloc_coherent() are always zeroed
on most architectures. 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 ARM architecture with other
implementations by unconditionally zeroing allocated buffer.Also to fix
dma_zalloc_coherent behavior.

Reported-by: Sean Wang <sean.wang@...iatek.com>
Signed-off-by: YueHaibing <yuehaibing@...wei.com>
Reviewed-by: zhong jiang <zhongjiang@...wei.com>
---
v2: reference more argument from arm64 commit as Christoph suggested
---
 arch/arm/mm/dma-mapping.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 6656647..cf5882f 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -564,6 +564,7 @@ static void *__alloc_from_pool(size_t size, struct page **ret_page)

 		*ret_page = phys_to_page(phys);
 		ptr = (void *)val;
+		memset(ptr, 0, size);
 	}

 	return ptr;
-- 
2.7.0