linux-kernel - Re: [PATCH] ARM: mm: fix the boundary checking on bitmaps

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Date:	Mon, 14 Jul 2014 15:02:48 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	Haojian Zhuang <haojian.zhuang@...aro.org>, linux@....linux.org.uk,
	will.deacon@....com, andreas.herrmann@...xeda.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: mm: fix the boundary checking on bitmaps

Hello,

On 2014-07-10 04:28, Haojian Zhuang wrote:
> The issue of boundary checking on bitmaps is introduced by this commit
> in below.
>
> commit 4d852ef8c2544ce21ae41414099a7504c61164a0
> Author: Andreas Herrmann <andreas.herrmann@...xeda.com>
> Date:   Tue Feb 25 13:09:53 2014 +0100
>
>      arm: dma-mapping: Add support to extend DMA IOMMU mappings
>
> Multiple bitmaps were introduced as extension. If it needs to extend
> a bitmap, it still check whether the allocation exceeding the total
> size, not current bitmap size. So change the condition from
> mapping->bits to PAGE_SIZE.
>
> Signed-off-by: Haojian Zhuang <haojian.zhuang@...aro.org>

NACK, this patch is not correct. mapping->bits contains the correct size of
a single bitmap, see the beginning of arm_iommu_create_mapping() function.

> ---
>   arch/arm/mm/dma-mapping.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 4c88935..d7da5c3 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -1089,9 +1089,9 @@ static inline dma_addr_t __alloc_iova(struct dma_iommu_mapping *mapping,
>   	spin_lock_irqsave(&mapping->lock, flags);
>   	for (i = 0; i < mapping->nr_bitmaps; i++) {
>   		start = bitmap_find_next_zero_area(mapping->bitmaps[i],
> -				mapping->bits, 0, count, align);
> +				PAGE_SIZE, 0, count, align);
>   
> -		if (start > mapping->bits)
> +		if (start > PAGE_SIZE)
>   			continue;
>   
>   		bitmap_set(mapping->bitmaps[i], start, count);
> @@ -1110,9 +1110,9 @@ static inline dma_addr_t __alloc_iova(struct dma_iommu_mapping *mapping,
>   		}
>   
>   		start = bitmap_find_next_zero_area(mapping->bitmaps[i],
> -				mapping->bits, 0, count, align);
> +				PAGE_SIZE, 0, count, align);
>   
> -		if (start > mapping->bits) {
> +		if (start > PAGE_SIZE) {
>   			spin_unlock_irqrestore(&mapping->lock, flags);
>   			return DMA_ERROR_CODE;
>   		}

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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