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

From: Mark Rutland
Date: Tue Dec 06 2016 - 13:21:21 EST


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
>