linux-kernel - Re: [PATCH v3] sh: mm: Fix unprotected access to struct device

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Date:   Wed, 2 May 2018 09:46:31 +0200
From:   jacopo mondi <jacopo@...ndi.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     ysato@...rs.sourceforge.jp, dalias@...c.org,
        thomas.petazzoni@...e-electrons.com, robin.murphy@....com,
        geert@...ux-m68k.org, sergei.shtylyov@...entembedded.com,
        linux-renesas-soc@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] sh: mm: Fix unprotected access to struct device

Hi again Christoph,

    The gentle ping actually applies to this version of the patch.

Sorry for the confusion.
Thanks
   j

On Wed, Apr 18, 2018 at 11:42:35AM +0200, Jacopo Mondi wrote:
> With commit ce88313069c36eef80f21fd7 ("arch/sh: make the DMA mapping
> operations observe dev->dma_pfn_offset") the generic DMA allocation
> function on which the SH 'dma_alloc_coherent()' function relies on,
> accesses the 'dma_pfn_offset' field of struct device.
>
> Unfortunately the 'dma_generic_alloc_coherent()' function is called from
> several places with a NULL struct device argument, halting the CPU
> during the boot process.
>
> This patch fixes the issue by protecting access to dev->dma_pfn_offset,
> with a trivial check for validity. It also passes a valid 'struct device'
> in the 'platform_resource_setup_memory()' function which is the main user
> of 'dma_alloc_coherent()', and inserts a WARN_ON() check to remind to future
> (and existing) bogus users of this function to provide a valid 'struct device'
> whenever possible.
>
> Fixes: ce88313069c36eef80f21fd7 ("arch/sh: make the DMA mapping operations observe dev->dma_pfn_offset")
> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Reviewed-by: Thomas Petazzoni <thomas.petazzoni@...tlin.com>
>
> ---
> v2 -> v3:
> - remove (now) useless parenthesis around pfn assignement as suggested
>   by Sergei
> - Add changelog to the patch, which I forgot in v2
>
> v1 -> v2:
> - Move WARN_ON() closer to dev validity check as suggested by Geert
>
> ---
>  arch/sh/mm/consistent.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/sh/mm/consistent.c b/arch/sh/mm/consistent.c
> index 8ce9869..f1b4469 100644
> --- a/arch/sh/mm/consistent.c
> +++ b/arch/sh/mm/consistent.c
> @@ -59,7 +59,9 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size,
>
>  	split_page(pfn_to_page(virt_to_phys(ret) >> PAGE_SHIFT), order);
>
> -	*dma_handle = virt_to_phys(ret) - PFN_PHYS(dev->dma_pfn_offset);
> +	*dma_handle = virt_to_phys(ret);
> +	if (!WARN_ON(!dev))
> +		*dma_handle -= PFN_PHYS(dev->dma_pfn_offset);
>
>  	return ret_nocache;
>  }
> @@ -69,9 +71,12 @@ void dma_generic_free_coherent(struct device *dev, size_t size,
>  			       unsigned long attrs)
>  {
>  	int order = get_order(size);
> -	unsigned long pfn = (dma_handle >> PAGE_SHIFT) + dev->dma_pfn_offset;
> +	unsigned long pfn = dma_handle >> PAGE_SHIFT;
>  	int k;
>
> +	if (!WARN_ON(!dev))
> +		pfn += dev->dma_pfn_offset;
> +
>  	for (k = 0; k < (1 << order); k++)
>  		__free_pages(pfn_to_page(pfn + k), 0);
>
> @@ -143,7 +148,7 @@ int __init platform_resource_setup_memory(struct platform_device *pdev,
>  	if (!memsize)
>  		return 0;
>
> -	buf = dma_alloc_coherent(NULL, memsize, &dma_handle, GFP_KERNEL);
> +	buf = dma_alloc_coherent(&pdev->dev, memsize, &dma_handle, GFP_KERNEL);
>  	if (!buf) {
>  		pr_warning("%s: unable to allocate memory\n", name);
>  		return -ENOMEM;
> --
> 2.7.4
>

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