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

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Date:   Tue, 29 Nov 2016 11:39:44 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <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" 
        <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 AM, Laura Abbott <labbott@...hat.com> 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>

Acked-by: Kees Cook <keescook@...omium.org>

I should probably add a corresponding alias test to lkdtm...

-Kees

> ---
> 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
>



-- 
Kees Cook
Nexus Security