linux-kernel - Re: [PATCH] mm: do not export ioremap_page

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Date:   Sun, 22 Jan 2017 14:25:36 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     zhongjiang <zhongjiang@...wei.com>, <akpm@...ux-foundation.org>,
        <minchan@...nel.org>, <mhocko@...nel.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: do not export ioremap_page_range symbol for external
 module

On 01/22/2017 04:58 AM, zhongjiang wrote:
> From: zhong jiang <zhongjiang@...wei.com>
>
> Recently, I find the ioremap_page_range had been abusing. The improper
> address mapping is a issue. it will result in the crash. so, remove
> the symbol. It can be replaced by the ioremap_cache or others symbol.

Hi Zhong,

After thinking about this for a bit, and looking through our own (out-of-tree) kernel modules, I 
think you have a good point. I just can't see any reason for a driver to call ioremap_page_range 
directly. So the code change looks good to me.

For the commit description, here is a proposed re-wording, optional, that perhaps may be a little 
clearer. See if you like it?

-------
Recently, I've found cases in which ioremap_page_range was used incorrectly, in external modules, 
leading to crashes. This can be partly attributed to the fact that ioremap_page_range is 
lower-level, with fewer protections, as compared to the other functions that an external module 
would typically call. Those include:

         ioremap_cache
         ioremap_nocache
         ioremap_prot
         ioremap_uc
         ioremap_wc
         ioremap_wt

...each of which wraps __ioremap_caller, which in turn provides a safer way to achieve the mapping.

Therefore, stop EXPORT-ing ioremap_page_range.
-------

I may get some heat for this if another out-of-tree driver needs that symbol, but if no one else 
pops up and shrieks, you can add:

Reviewed-by: John Hubbard <jhubbard@...dia.com>

thanks,
john h


>
> Signed-off-by: zhong jiang <zhongjiang@...wei.com>
> ---
>  lib/ioremap.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/lib/ioremap.c b/lib/ioremap.c
> index 86c8911..a3e14ce 100644
> --- a/lib/ioremap.c
> +++ b/lib/ioremap.c
> @@ -144,4 +144,3 @@ int ioremap_page_range(unsigned long addr,
>
>  	return err;
>  }
> -EXPORT_SYMBOL_GPL(ioremap_page_range);
> --
> 1.8.3.1
>