Re: [PATCH 2/4] dma-direct: leak memory that can't be re-encrypted

[David Rientjes via iommu <iommu@lists.linux-foundation.org>]

On Tue, 19 Oct 2021, Christoph Hellwig wrote:

> We must never unencryped memory go back into the general page pool.
> So if we fail to set it back to encrypted when freeing DMA memory, leak
> the memory insted and warn the user.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  kernel/dma/direct.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 96f02248e7fa2..6673f7aebf787 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -264,9 +264,11 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>  	return ret;
>  
>  out_encrypt_pages:
> -	/* If memory cannot be re-encrypted, it must be leaked */
> -	if (dma_set_encrypted(dev, page_address(page), size))
> +	if (dma_set_encrypted(dev, page_address(page), size)) {
> +		pr_warn_ratelimited(
> +			"leaking DMA memory that can't be re-encrypted\n");
>  		return NULL;
> +	}
>  out_free_pages:
>  	__dma_direct_free_pages(dev, page, size);
>  	return NULL;
> @@ -305,7 +307,11 @@ void dma_direct_free(struct device *dev, size_t size,
>  	    dma_free_from_pool(dev, cpu_addr, PAGE_ALIGN(size)))
>  		return;
>  
> -	dma_set_encrypted(dev, cpu_addr, 1 << page_order);
> +	if (dma_set_encrypted(dev, cpu_addr, 1 << page_order)) {
> +		pr_warn_ratelimited(
> +			"leaking DMA memory that can't be re-encrypted\n");
> +		return;
> +	}
>  
>  	if (IS_ENABLED(CONFIG_DMA_REMAP) && is_vmalloc_addr(cpu_addr))
>  		vunmap(cpu_addr);
> @@ -363,7 +369,10 @@ void dma_direct_free_pages(struct device *dev, size_t size,
>  	    dma_free_from_pool(dev, vaddr, size))
>  		return;
>  
> -	dma_set_encrypted(dev, vaddr, 1 << page_order);
> +	if (dma_set_encrypted(dev, vaddr, 1 << page_order)) {
> +		pr_warn_ratelimited(
> +			"leaking DMA memory that can't be re-encrypted\n");
> +	}

Is this actually leaking the memory?

>  	__dma_direct_free_pages(dev, page, size);
>  }
>  
> -- 
> 2.30.2
> 
> 
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