linux-kernel - Re: [PATCH] misc: lkdtm: Add volatile to intentional NULL pointer reference

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Sat, 15 Apr 2017 10:41:28 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Matthias Kaehlcke <mka@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Grant Grundler <grundler@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Michael Davidson <md@...gle.com>
Subject: Re: [PATCH] misc: lkdtm: Add volatile to intentional NULL pointer reference

On Fri, Apr 14, 2017 at 2:15 PM, Matthias Kaehlcke <mka@...omium.org> wrote:
> From: Michael Davidson <md@...gle.com>
>
> Add a volatile qualifier where a NULL pointer is deliberately
> dereferenced to trigger a panic.
>
> Without the volatile qualifier clang will issue the following warning:
> "indirection of non-volatile null pointer will be deleted,
> not trap [-Wnull-dereference]" and replace the pointer reference
> with a __builtin_trap() (which generates a ud2 instruction on x86_64).
>
> Signed-off-by: Michael Davidson <md@...gle.com>
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>

Thanks!

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

Greg, please add this to drivers/misc when you get a chance. :)

-Kees

> ---
>  drivers/misc/lkdtm_bugs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/misc/lkdtm_bugs.c b/drivers/misc/lkdtm_bugs.c
> index e3f4cd8876b5..d734d75afade 100644
> --- a/drivers/misc/lkdtm_bugs.c
> +++ b/drivers/misc/lkdtm_bugs.c
> @@ -67,7 +67,7 @@ void lkdtm_WARNING(void)
>
>  void lkdtm_EXCEPTION(void)
>  {
> -       *((int *) 0) = 0;
> +       *((volatile int *) 0) = 0;
>  }
>
>  void lkdtm_LOOP(void)
> --
> 2.12.2.762.g0e3151a226-goog
>



-- 
Kees Cook
Pixel Security