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

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Date:   Wed, 18 Apr 2018 12:13:10 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        ysato@...rs.sourceforge.jp, dalias@...c.org,
        thomas.petazzoni@...e-electrons.com, robin.murphy@....com
Cc:     geert@...ux-m68k.org, linux-renesas-soc@...r.kernel.org,
        linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sh: mm: Fix unprotected access to struct device

Hello!

On 4/17/2018 4:35 PM, 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,
> access 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 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 inserting a WARN_ON() check to make future
> (and existing) bogus users of this function they're should 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>
> ---
>   arch/sh/mm/consistent.c | 15 ++++++++++++---
>   1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/sh/mm/consistent.c b/arch/sh/mm/consistent.c
> index 8ce9869..b257155 100644
> --- a/arch/sh/mm/consistent.c
> +++ b/arch/sh/mm/consistent.c
[...]
> @@ -69,9 +73,14 @@ 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);

    Parens no longer needed...

[...]

MBR, Sergei