linux-kernel - Re: [PATCH v4 2/9] arch/arm/mm/dma-mapping.c: Convert to use vm_insert

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Date:   Tue, 18 Dec 2018 09:37:54 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     akpm@...ux-foundation.org, willy@...radead.org, mhocko@...e.com,
        robin.murphy@....com, iamjoonsoo.kim@....com, treding@...dia.com,
        keescook@...omium.org, m.szyprowski@...sung.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 2/9] arch/arm/mm/dma-mapping.c: Convert to use
 vm_insert_range

On Tue, Dec 18, 2018 at 01:52:09AM +0530, Souptick Joarder wrote:
> Convert to use vm_insert_range() to map range of kernel
> memory to user vma.
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> ---
>  arch/arm/mm/dma-mapping.c | 21 +++++++--------------
>  1 file changed, 7 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 661fe48..7cbcde5 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -1582,31 +1582,24 @@ static int __arm_iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma
>  		    void *cpu_addr, dma_addr_t dma_addr, size_t size,
>  		    unsigned long attrs)
>  {
> -	unsigned long uaddr = vma->vm_start;
> -	unsigned long usize = vma->vm_end - vma->vm_start;
> +	unsigned long page_count = vma_pages(vma);
>  	struct page **pages = __iommu_get_pages(cpu_addr, attrs);
>  	unsigned long nr_pages = PAGE_ALIGN(size) >> PAGE_SHIFT;
>  	unsigned long off = vma->vm_pgoff;
> +	int err;
>  
>  	if (!pages)
>  		return -ENXIO;
>  
> -	if (off >= nr_pages || (usize >> PAGE_SHIFT) > nr_pages - off)
> +	if (off >= nr_pages)
>  		return -ENXIO;

Are you sure you can make this change?

You are restricting the offset to be within 0..nr_pages which ensures
that the initial struct page that is passed to vm_insert_range() is
valid, but I think the removal of the following check is unsafe.

Your new vm_insert_range() function only checks page_count <=
vma_pages(vma), which it will be since it _is_ vma_pages(vma).  With
the removal of the second condition, there will be nothing checking
that (eg) off may be nr_pages - 1, and page_count=50, meaning that
vm_insert_range() will walk off the end of the page array.

Please take another look at this.

What about the other callsites of your new function - do they have
the same issue?

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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