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Automatic variable initialization updates for v5.9-rc1

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- Introduce CONFIG_INIT_STACK_ALL_ZERO (Alexander Potapenko)
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Merge tag 'var-init-v5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull automatic variable initialization updates from Kees Cook:
 "This adds the "zero" init option from Clang, which is being used
  widely in production builds of Android and Chrome OS (though it also
  keeps the "pattern" init, which is better for debug builds).

   - Introduce CONFIG_INIT_STACK_ALL_ZERO (Alexander Potapenko)"

* tag 'var-init-v5.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  security: allow using Clang's zero initialization for stack variables
This commit is contained in:
Linus Torvalds 2020-08-04 13:38:35 -07:00
commit 5b5d3be5d6
3 changed files with 43 additions and 11 deletions
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13
Makefile
View File

@ -803,11 +803,20 @@ KBUILD_CFLAGS += -fomit-frame-pointer
endif
endif
# Initialize all stack variables with a pattern, if desired.
ifdef CONFIG_INIT_STACK_ALL
# Initialize all stack variables with a 0xAA pattern.
ifdef CONFIG_INIT_STACK_ALL_PATTERN
KBUILD_CFLAGS += -ftrivial-auto-var-init=pattern
endif
# Initialize all stack variables with a zero value.
ifdef CONFIG_INIT_STACK_ALL_ZERO
# Future support for zero initialization is still being debated, see
# https://bugs.llvm.org/show_bug.cgi?id=45497. These flags are subject to being
# renamed or dropped.
KBUILD_CFLAGS += -ftrivial-auto-var-init=zero
KBUILD_CFLAGS += -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
endif
DEBUG_CFLAGS := $(call cc-option, -fno-var-tracking-assignments)
ifdef CONFIG_DEBUG_INFO

12
init/main.c
View File

@ -779,14 +779,16 @@ static void __init report_meminit(void)
{
const char *stack;
if (IS_ENABLED(CONFIG_INIT_STACK_ALL))
stack = "all";
if (IS_ENABLED(CONFIG_INIT_STACK_ALL_PATTERN))
stack = "all(pattern)";
else if (IS_ENABLED(CONFIG_INIT_STACK_ALL_ZERO))
stack = "all(zero)";
else if (IS_ENABLED(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL))
stack = "byref_all";
stack = "byref_all(zero)";
else if (IS_ENABLED(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF))
stack = "byref";
stack = "byref(zero)";
else if (IS_ENABLED(CONFIG_GCC_PLUGIN_STRUCTLEAK_USER))
stack = "__user";
stack = "__user(zero)";
else
stack = "off";

29
security/Kconfig.hardening
View File

@ -19,13 +19,16 @@ config GCC_PLUGIN_STRUCTLEAK
menu "Memory initialization"
config CC_HAS_AUTO_VAR_INIT
config CC_HAS_AUTO_VAR_INIT_PATTERN
def_bool $(cc-option,-ftrivial-auto-var-init=pattern)
config CC_HAS_AUTO_VAR_INIT_ZERO
def_bool $(cc-option,-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang)
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_ALL_PATTERN if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT_PATTERN
default INIT_STACK_NONE
help
This option enables initialization of stack variables at
@ -88,9 +91,9 @@ choice
of uninitialized stack variable exploits and information
exposures.
config INIT_STACK_ALL
config INIT_STACK_ALL_PATTERN
bool "0xAA-init everything on the stack (strongest)"
depends on CC_HAS_AUTO_VAR_INIT
depends on CC_HAS_AUTO_VAR_INIT_PATTERN
help
Initializes everything on the stack with a 0xAA
pattern. This is intended to eliminate all classes
@ -98,6 +101,24 @@ choice
exposures, even variables that were warned to have been
left uninitialized.
Pattern initialization is known to provoke many existing bugs
related to uninitialized locals, e.g. pointers receive
non-NULL values, buffer sizes and indices are very big.
config INIT_STACK_ALL_ZERO
bool "zero-init everything on the stack (strongest and safest)"
depends on CC_HAS_AUTO_VAR_INIT_ZERO
help
Initializes everything on the stack with a zero
value. 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.
Zero initialization provides safe defaults for strings,
pointers, indices and sizes, and is therefore
more suitable as a security mitigation measure.
endchoice
config GCC_PLUGIN_STRUCTLEAK_VERBOSE