linux-kernel - Re: [PATCH] Let CONFIG_STRICT_DEVMEM depends on CONFIG

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Date:   Thu, 6 Oct 2016 14:39:31 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Dave Young <dyoung@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Tejun Heo <tj@...nel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH] Let CONFIG_STRICT_DEVMEM depends on CONFIG_DEVMEM

On Wed, Oct 5, 2016 at 10:12 PM, Dave Young <dyoung@...hat.com> wrote:
> With CONFIG_DEVMEM not set, CONFIG_STRICT_DEVMEM will be useless
> even if it is set =y, thus let's update the dependency in Kconfig.
>
> Signed-off-by: Dave Young <dyoung@...hat.com>

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

> ---
>  lib/Kconfig.debug |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --- linux-x86.orig/lib/Kconfig.debug
> +++ linux-x86/lib/Kconfig.debug
> @@ -1980,7 +1980,7 @@ config ARCH_HAS_DEVMEM_IS_ALLOWED
>
>  config STRICT_DEVMEM
>         bool "Filter access to /dev/mem"
> -       depends on MMU
> +       depends on MMU && DEVMEM
>         depends on ARCH_HAS_DEVMEM_IS_ALLOWED
>         default y if TILE || PPC
>         ---help---

While we're at it, can we make DEVKMEM default=n? The help text even
suggests making it "n".

-Kees

-- 
Kees Cook
Nexus Security