linux-kernel - Re: [PATCHv4 09/10] mm/usercopy: Switch to using lm

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Date:   Tue, 6 Dec 2016 18:20:28 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv4 09/10] mm/usercopy: Switch to using lm_alias

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@...hat.com>

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

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
>