From: Alexander Potapenko <glider@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>,
James Morris <jmorris@namei.org>,
Alexander Popov <alex.popov@linux.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Kostya Serebryany <kcc@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
Sandeep Patil <sspatil@android.com>,
Laura Abbott <labbott@redhat.com>,
Randy Dunlap <rdunlap@infradead.org>,
Michal Marek <michal.lkml@markovi.net>,
Emese Revfy <re.emese@gmail.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
linux-security-module <linux-security-module@vger.kernel.org>,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 3/3] security: Implement Clang's stack initialization
Date: Fri, 12 Apr 2019 13:36:12 +0200 [thread overview]
Message-ID: <CAG_fn=VqXUTF+rLPcGNR8=kmNFdSAqmMKb9r9=SkoDcg7RrKnQ@mail.gmail.com> (raw)
In-Reply-To: <20190411180117.27704-4-keescook@chromium.org>
On Thu, Apr 11, 2019 at 8:01 PM Kees Cook <keescook@chromium.org> wrote:
>
> CONFIG_INIT_STACK_ALL turns on stack initialization based on
> -ftrivial-auto-var-init in Clang builds, which has greater coverage
> than CONFIG_GCC_PLUGINS_STRUCTLEAK_BYREF_ALL.
>
> -ftrivial-auto-var-init Clang option provides trivial initializers for
> uninitialized local variables, variable fields and padding.
>
> It has three possible values:
> pattern - uninitialized locals are filled with a fixed pattern
> (mostly 0xAA on 64-bit platforms, see https://reviews.llvm.org/D54604
> for more details, but 0x000000AA for 32-bit pointers) likely to cause
> crashes when uninitialized value is used;
> zero (it's still debated whether this flag makes it to the official
> Clang release) - uninitialized locals are filled with zeroes;
> uninitialized (default) - uninitialized locals are left intact.
>
> This patch uses only the "pattern" mode when CONFIG_INIT_STACK_ALL is
> enabled.
>
> Developers have the possibility to opt-out of this feature on a
> per-variable basis by using __attribute__((uninitialized)), but such
> use should be well justified in comments.
>
> Co-developed-by: Alexander Potapenko <glider@google.com>
> Signed-off-by: Alexander Potapenko <glider@google.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Alexander Potapenko <glider@google.com>
> ---
> Makefile | 5 +++++
> security/Kconfig.hardening | 15 ++++++++++++++-
> 2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index c0a34064c574..a7d9c6cd0267 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -745,6 +745,11 @@ KBUILD_CFLAGS += -fomit-frame-pointer
> endif
> endif
>
> +# Initialize all stack variables with a pattern, if desired.
> +ifdef CONFIG_INIT_STACK_ALL
> +KBUILD_CFLAGS += -ftrivial-auto-var-init=pattern
> +endif
> +
> DEBUG_CFLAGS := $(call cc-option, -fno-var-tracking-assignments)
>
> ifdef CONFIG_DEBUG_INFO
> diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> index 3dd7a28c3822..5dd61770d3f0 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -18,9 +18,12 @@ config GCC_PLUGIN_STRUCTLEAK
>
> menu "Memory initialization"
>
> +config CC_HAS_AUTO_VAR_INIT
> + def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
> +
> choice
> prompt "Initialize kernel stack variables at function entry"
> - depends on GCC_PLUGINS
> + depends on CC_HAS_AUTO_VAR_INIT || GCC_PLUGINS
> default INIT_STACK_NONE
> help
> This option enables initialization of stack variables at
> @@ -76,6 +79,16 @@ choice
> of uninitialized stack variable exploits and information
> exposures.
>
> + config INIT_STACK_ALL
> + bool "0xAA-init everything on the stack (strongest)"
> + depends on CC_HAS_AUTO_VAR_INIT
> + help
> + Initializes everything on the stack with a 0xAA
> + pattern. This is intended to eliminate all classes
> + of uninitialized stack variable exploits and information
> + exposures, even variables that were warned to have been
> + left uninitialized.
> +
> endchoice
>
> config GCC_PLUGIN_STRUCTLEAK_VERBOSE
> --
> 2.17.1
>
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
prev parent reply other threads:[~2019-04-12 11:36 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-11 18:01 [PATCH v2 0/3] Refactor memory initialization hardening Kees Cook
2019-04-11 18:01 ` [PATCH v2 1/3] security: Create "kernel hardening" config area Kees Cook
2019-04-12 1:38 ` Masahiro Yamada
2019-04-23 19:36 ` Kees Cook
2019-04-24 4:05 ` Masahiro Yamada
2019-04-15 16:44 ` Alexander Popov
2019-04-16 4:02 ` Kees Cook
2019-04-16 13:55 ` Alexander Popov
2019-04-16 13:56 ` Kees Cook
2019-04-19 19:15 ` Alexander Popov
2019-04-11 18:01 ` [PATCH v2 2/3] security: Move stackleak config to Kconfig.hardening Kees Cook
2019-04-11 18:01 ` [PATCH v2 3/3] security: Implement Clang's stack initialization Kees Cook
2019-04-12 11:36 ` Alexander Potapenko [this message]
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