linux-kernel - Re: [PATCH 5/6] notifiers: Use CHECK_DATA

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Message-ID: <CAGXu5jJv7ipL+Ang+AWeoUEYapjTH3sKUuSZFKWQWyTSmswwWQ@mail.gmail.com>
Date:   Wed, 22 Mar 2017 12:29:24 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Arjan van de Ven <arjan@...ux.intel.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Olof Johansson <olof@...om.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 5/6] notifiers: Use CHECK_DATA_CORRUPTION() on checks

On Mon, Mar 6, 2017 at 11:09 AM, Kees Cook <keescook@...omium.org> wrote:
> When performing notifier function pointer sanity checking, allow
> CONFIG_BUG_ON_DATA_CORRUPTION to upgrade from a WARN to a BUG.
> Additionally enables CONFIG_DEBUG_NOTIFIERS when selecting
> CONFIG_BUG_ON_DATA_CORRUPTION.

Any feedback on this change? By default, this retains the existing
WARN behavior...

-Kees

>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  kernel/notifier.c | 5 +++--
>  lib/Kconfig.debug | 3 ++-
>  2 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/notifier.c b/kernel/notifier.c
> index 6196af8a8223..58cc14958d92 100644
> --- a/kernel/notifier.c
> +++ b/kernel/notifier.c
> @@ -84,8 +84,9 @@ static int notifier_call_chain(struct notifier_block **nl,
>                 next_nb = rcu_dereference_raw(nb->next);
>
>  #ifdef CONFIG_DEBUG_NOTIFIERS
> -               if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
> -                       WARN(1, "Invalid notifier called!");
> +               if (CHECK_DATA_CORRUPTION(
> +                               !func_ptr_is_kernel_text(nb->notifier_call),
> +                               "Invalid notifier called!")) {
>                         nb = next_nb;
>                         continue;
>                 }
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 42c61cfe7d19..70e9f2c1bb30 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1277,7 +1277,7 @@ config DEBUG_SG
>
>  config DEBUG_NOTIFIERS
>         bool "Debug notifier call chains"
> -       depends on DEBUG_KERNEL
> +       depends on DEBUG_KERNEL || BUG_ON_DATA_CORRUPTION
>         help
>           Enable this to turn on sanity checking for notifier call chains.
>           This is most useful for kernel developers to make sure that
> @@ -1995,6 +1995,7 @@ config BUG_ON_DATA_CORRUPTION
>         bool "Trigger a BUG when data corruption is detected"
>         select DEBUG_CREDENTIALS
>         select DEBUG_LIST
> +       select DEBUG_NOTIFIERS
>         select DEBUG_SG
>         help
>           This option enables several inexpensive data corruption checks.
> --
> 2.7.4
>



-- 
Kees Cook
Pixel Security