Re: [PATCH] arm64: Do not leave an invalid area->pages pointer in dma_common_contiguous_remap()

[Robin Murphy]

On 25/04/17 19:22, Catalin Marinas wrote:
> The dma_common_pages_remap() function allocates a vm_struct object and
> initialises the pages pointer to value passed as argument. However, when
> this function is called dma_common_contiguous_remap(), the pages array
> is only temporarily allocated, being freed shortly after
> dma_common_contiguous_remap() returns. Architecture code checking the
> validity of an area->pages pointer would incorrectly dereference already
> freed pointers. This has been exposed by the arm64 commit 44176bb38fa4
> ("arm64: Add support for DMA_ATTR_FORCE_CONTIGUOUS to IOMMU").
> 
> Fixes: 513510ddba96 ("common: dma-mapping: introduce common remapping functions")
> Cc: Laura Abbott <labbott@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Reported-by: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> ---
> 
> This is for correctness since once the arm64's mmap and get_sgtable ops
> are fixed for DMA_ATTR_FORCE_CONTIGUOUS, we would no longer see the
> issue. Anyway, it's better to get this fixed in case others trip over a
> similar issue. I added a "Fixes" tag for completeness but I'm not sure
> it's worth back-porting.
> 
>  drivers/base/dma-mapping.c | 29 ++++++++++++++++++++++-------
>  1 file changed, 22 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
> index efd71cf4fdea..ab7071041141 100644
> --- a/drivers/base/dma-mapping.c
> +++ b/drivers/base/dma-mapping.c
> @@ -277,8 +277,8 @@ EXPORT_SYMBOL(dma_common_mmap);
>   * remaps an array of PAGE_SIZE pages into another vm_area
>   * Cannot be used in non-sleeping contexts
>   */

Nit: the above comment ends up in the wrong place now (it should still
belong to dma_common_pages_remap()).

Otherwise,

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

> -void *dma_common_pages_remap(struct page **pages, size_t size,
> -			unsigned long vm_flags, pgprot_t prot,
> +static struct vm_struct *__dma_common_pages_remap(struct page **pages,
> +			size_t size, unsigned long vm_flags, pgprot_t prot,
>  			const void *caller)
>  {
>  	struct vm_struct *area;
> @@ -287,13 +287,26 @@ void *dma_common_pages_remap(struct page **pages, size_t size,
>  	if (!area)
>  		return NULL;
>  
> -	area->pages = pages;
> -
>  	if (map_vm_area(area, prot, pages)) {
>  		vunmap(area->addr);
>  		return NULL;
>  	}
>  
> +	return area;
> +}
> +
> +void *dma_common_pages_remap(struct page **pages, size_t size,
> +			unsigned long vm_flags, pgprot_t prot,
> +			const void *caller)
> +{
> +	struct vm_struct *area;
> +
> +	area = __dma_common_pages_remap(pages, size, vm_flags, prot, caller);
> +	if (!area)
> +		return NULL;
> +
> +	area->pages = pages;
> +
>  	return area->addr;
>  }
>  
> @@ -308,7 +321,7 @@ void *dma_common_contiguous_remap(struct page *page, size_t size,
>  {
>  	int i;
>  	struct page **pages;
> -	void *ptr;
> +	struct vm_struct *area;
>  	unsigned long pfn;
>  
>  	pages = kmalloc(sizeof(struct page *) << get_order(size), GFP_KERNEL);
> @@ -318,11 +331,13 @@ void *dma_common_contiguous_remap(struct page *page, size_t size,
>  	for (i = 0, pfn = page_to_pfn(page); i < (size >> PAGE_SHIFT); i++)
>  		pages[i] = pfn_to_page(pfn + i);
>  
> -	ptr = dma_common_pages_remap(pages, size, vm_flags, prot, caller);
> +	area = __dma_common_pages_remap(pages, size, vm_flags, prot, caller);
>  
>  	kfree(pages);
>  
> -	return ptr;
> +	if (!area)
> +		return NULL;
> +	return area->addr;
>  }
>  
>  /*
>