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[173.164.112.133]) by smtp.gmail.com with ESMTPSA id r145sm92291798pgr.84.2019.04.11.11.01.25 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 11 Apr 2019 11:01:25 -0700 (PDT) From: Kees Cook To: Alexander Potapenko Cc: Kees Cook , Masahiro Yamada , James Morris , Alexander Popov , Nick Desaulniers , Kostya Serebryany , Dmitry Vyukov , Sandeep Patil , Laura Abbott , Randy Dunlap , Michal Marek , Emese Revfy , "Serge E. Hallyn" , kernel-hardening@lists.openwall.com, linux-security-module@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 3/3] security: Implement Clang's stack initialization Date: Thu, 11 Apr 2019 11:01:17 -0700 Message-Id: <20190411180117.27704-4-keescook@chromium.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190411180117.27704-1-keescook@chromium.org> References: <20190411180117.27704-1-keescook@chromium.org> Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 Signed-off-by: Alexander Potapenko Signed-off-by: Kees Cook Tested-by: Alexander Potapenko --- 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