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authorKees Cook <keescook@chromium.org>2019-04-10 18:48:31 +0300
committerKees Cook <keescook@chromium.org>2019-04-25 00:00:56 +0300
commit709a972efb01efaeb97cad1adc87fe400119c8ab (patch)
tree395292ab51f012c21b436c404811e810bc863b4d
parentb6a6a3772d20b8552e703bb2a651760a22167cf6 (diff)
downloadlinux-709a972efb01efaeb97cad1adc87fe400119c8ab.tar.xz
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@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> Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
-rw-r--r--Makefile5
-rw-r--r--security/Kconfig.hardening14
2 files changed, 19 insertions, 0 deletions
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 a96d4a43ca65..0a1d4ca314f4 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -18,9 +18,13 @@ 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"
default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS
+ default INIT_STACK_ALL if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT
default INIT_STACK_NONE
help
This option enables initialization of stack variables at
@@ -76,6 +80,16 @@ 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