Re: [PATCH] mm: do not export ioremap_page_range symbol for external module

[John Hubbard]

On 01/22/2017 04:58 AM, zhongjiang wrote:
> From: zhong jiang <zhongjiang@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>

thanks,
john h


> Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx>
> ---
>  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