linux-kernel - Re: [PATCH v2] drivers/firmware/broadcom/bcm47xx_nvram.c: fix incorrect __ioread32

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Date:	Wed, 23 Mar 2016 22:43:59 +0100
From:	Hauke Mehrtens <hauke@...ke-m.de>
To:	Aaro Koskinen <aaro.koskinen@....fi>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Rafał Miłecki <zajec5@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drivers/firmware/broadcom/bcm47xx_nvram.c: fix
 incorrect __ioread32_copy

On 03/16/2016 12:06 AM, Aaro Koskinen wrote:
> Commit 1f330c327900 ("drivers/firmware/broadcom/bcm47xx_nvram.c: use
> __ioread32_copy() instead of open-coding") switched to use a generic copy
> function, but failed to notice that the header pointer is updated between
> the two copies, resulting in bogus data being copied in the latter one.
> Fix by keeping the old header pointer.
> 
> The patch fixes totally broken networking on WRT54GL router (both LAN
> and WLAN interfaces fail to probe).
> 
> Fixes: 1f330c327900 ("drivers/firmware/broadcom/bcm47xx_nvram.c: use __ioread32_copy() instead of open-coding")
> Signed-off-by: Aaro Koskinen <aaro.koskinen@....fi>
> ---
> 
> 	v2: Avoid using the device memory after the first copy when
> 	    checking the nvram length, suggested by Stephen Boyd.
> 
> 	v1: http://marc.info/?t=145807850800003&r=1&w=2
> 
>  drivers/firmware/broadcom/bcm47xx_nvram.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/firmware/broadcom/bcm47xx_nvram.c b/drivers/firmware/broadcom/bcm47xx_nvram.c
> index 0c2f0a6..0b631e5 100644
> --- a/drivers/firmware/broadcom/bcm47xx_nvram.c
> +++ b/drivers/firmware/broadcom/bcm47xx_nvram.c
> @@ -94,15 +94,14 @@ static int nvram_find_and_copy(void __iomem *iobase, u32 lim)
>  
>  found:
>  	__ioread32_copy(nvram_buf, header, sizeof(*header) / 4);
> -	header = (struct nvram_header *)nvram_buf;
> -	nvram_len = header->len;
> +	nvram_len = ((struct nvram_header *)(nvram_buf))->len;

I do not understand why this change is needed? Doesn't the old code do
exactly the same as the new one?

The old code updated the header pointer and then accesses a member, the
new one directly accesses this member without updating this pointer.

I assume, I am missing something. ;-)

>  	if (nvram_len > size) {
>  		pr_err("The nvram size according to the header seems to be bigger than the partition on flash\n");
>  		nvram_len = size;
>  	}
>  	if (nvram_len >= NVRAM_SPACE) {
>  		pr_err("nvram on flash (%i bytes) is bigger than the reserved space in memory, will just copy the first %i bytes\n",
> -		       header->len, NVRAM_SPACE - 1);
> +		       nvram_len, NVRAM_SPACE - 1);
>  		nvram_len = NVRAM_SPACE - 1;
>  	}
>  	/* proceed reading data after header */
>