Date: Thu, 11 Apr 2019 11:01:17 -0700 From: Kees Cook <keescook@...omium.org> To: Alexander Potapenko <glider@...gle.com> Cc: Kees Cook <keescook@...omium.org>, Masahiro Yamada <yamada.masahiro@...ionext.com>, James Morris <jmorris@...ei.org>, Alexander Popov <alex.popov@...ux.com>, Nick Desaulniers <ndesaulniers@...gle.com>, Kostya Serebryany <kcc@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Sandeep Patil <sspatil@...roid.com>, Laura Abbott <labbott@...hat.com>, Randy Dunlap <rdunlap@...radead.org>, Michal Marek <michal.lkml@...kovi.net>, Emese Revfy <re.emese@...il.com>, "Serge E. Hallyn" <serge@...lyn.com>, kernel-hardening@...ts.openwall.com, linux-security-module@...r.kernel.org, linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org Subject: [PATCH v2 3/3] security: Implement Clang's stack initialization 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@...gle.com> Signed-off-by: Alexander Potapenko <glider@...gle.com> Signed-off-by: Kees Cook <keescook@...omium.org> --- 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
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