Re: [PATCHv4 09/10] mm/usercopy: Switch to using lm_alias

[Mark Rutland]

On Tue, Nov 29, 2016 at 10:55:28AM -0800, Laura Abbott wrote:
> 
> The usercopy checking code currently calls __va(__pa(...)) to check for
> aliases on symbols. Switch to using lm_alias instead.
> 
> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>

I've given this a go on Juno, which boots happily. LKDTM triggers as
expected when copying from the kernel text and its alias.

Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
Tested-by: Mark Rutland <mark.rutland@xxxxxxx>

Thanks,
Mark.

> ---
> Found when reviewing the kernel. Tested.
> ---
>  mm/usercopy.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/usercopy.c b/mm/usercopy.c
> index 3c8da0a..8345299 100644
> --- a/mm/usercopy.c
> +++ b/mm/usercopy.c
> @@ -108,13 +108,13 @@ static inline const char *check_kernel_text_object(const void *ptr,
>  	 * __pa() is not just the reverse of __va(). This can be detected
>  	 * and checked:
>  	 */
> -	textlow_linear = (unsigned long)__va(__pa(textlow));
> +	textlow_linear = (unsigned long)lm_alias(textlow);
>  	/* No different mapping: we're done. */
>  	if (textlow_linear == textlow)
>  		return NULL;
>  
>  	/* Check the secondary mapping... */
> -	texthigh_linear = (unsigned long)__va(__pa(texthigh));
> +	texthigh_linear = (unsigned long)lm_alias(texthigh);
>  	if (overlaps(ptr, n, textlow_linear, texthigh_linear))
>  		return "<linear kernel text>";
>  
> -- 
> 2.7.4
>