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security: Implement Clang's stack initialization

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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>
This commit is contained in:
Kees Cook 2019-04-10 08:48:31 -07:00
parent b6a6a3772d
commit 709a972efb
2 changed files with 19 additions and 0 deletions
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5
Makefile
View File

@ -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

14
security/Kconfig.hardening
View File

@ -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