This patch is a part of a bigger initiative to allow initializing
heap/stack memory in the Linux kernels by default.
The rationale behind doing so is to reduce the severity of bugs caused
by using uninitialized memory.
CONFIG_INIT_ALL_MEMORY is going to be an umbrella config for options
that force heap and stack initialization.
CONFIG_INIT_ALL_STACK turns on stack initialization based on the
-ftrivial-auto-var-init Clang flag.
-ftrivial-auto-var-init is a Clang flag that 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) 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.
The proposed config builds the kernel with
-ftrivial-auto-var-init=pattern.
Developers have the possibility to opt-out of this feature on a
per-file (by using the INIT_ALL_MEMORY_ Makefile prefix) or per-variable
(by using __attribute__((uninitialized))) basis.
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: Kostya Serebryany <kcc@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Sandeep Patil <sspatil@xxxxxxxxxxx>
Cc: linux-security-module@xxxxxxxxxxxxxxx
Cc: linux-kbuild@xxxxxxxxxxxxxxx
---
Makefile | 3 ++-
scripts/Makefile.initmem | 17 +++++++++++++++++
scripts/Makefile.lib | 6 ++++++
security/Kconfig | 1 +
security/Kconfig.initmem | 22 ++++++++++++++++++++++
5 files changed, 48 insertions(+), 1 deletion(-)
create mode 100644 scripts/Makefile.initmem
create mode 100644 security/Kconfig.initmem
diff --git a/Makefile b/Makefile
index f070e0d65186..028ca37878fd 100644
--- a/Makefile
+++ b/Makefile
@@ -448,7 +448,7 @@ export HOSTCXX KBUILD_HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
-export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN
+export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN CFLAGS_INITMEM
export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
@@ -840,6 +840,7 @@ KBUILD_ARFLAGS := $(call ar-option,D)
include scripts/Makefile.kasan
include scripts/Makefile.extrawarn
include scripts/Makefile.ubsan
+include scripts/Makefile.initmem
# Add any arch overrides and user supplied CPPFLAGS, AFLAGS and CFLAGS as the
# last assignments
diff --git a/scripts/Makefile.initmem b/scripts/Makefile.initmem
new file mode 100644
index 000000000000..f49be398f2c1
--- /dev/null
+++ b/scripts/Makefile.initmem
@@ -0,0 +1,17 @@
+ifdef CONFIG_INIT_ALL_MEMORY
+
+# Clang's -ftrivial-auto-var-init=pattern flag initializes the
+# uninitialized parts of local variables (including fields and padding)
+# with a fixed pattern (0xAA in most cases).
+ifdef CONFIG_INIT_ALL_STACK
+ CFLAGS_INITMEM := -ftrivial-auto-var-init=pattern
+endif
+
+ifeq ($(call cc-option, $(CFLAGS_INITMEM) -Werror),)
+ ifneq ($(CONFIG_COMPILE_TEST),y)
+ $(warning Cannot use CONFIG_INIT_ALL_MEMORY: \
+ -ftrivial-auto-var-init is not supported by compiler)
+ endif
+endif
+
+endif
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 12b88d09c3a4..53d18fd15c79 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -131,6 +131,12 @@ _c_flags += $(if $(patsubst n%,, \
$(CFLAGS_UBSAN))
endif
+ifeq ($(CONFIG_INIT_ALL_MEMORY),y)
+_c_flags += $(if $(patsubst n%,, \
+ $(INIT_ALL_MEMORY_$(basetarget).o)$(INIT_ALL_MEMORY)y), \
+ $(CFLAGS_INITMEM))
+endif
+
ifeq ($(CONFIG_KCOV),y)
_c_flags += $(if $(patsubst n%,, \
$(KCOV_INSTRUMENT_$(basetarget).o)$(KCOV_INSTRUMENT)$(CONFIG_KCOV_INSTRUMENT_ALL)), \
diff --git a/security/Kconfig b/security/Kconfig
index e4fe2f3c2c65..cc12a39424dd 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -230,6 +230,7 @@ config STATIC_USERMODEHELPER_PATH
If you wish for all usermode helper programs to be disabled,
specify an empty string here (i.e. "").
+source "security/Kconfig.initmem"
source "security/selinux/Kconfig"
source "security/smack/Kconfig"
source "security/tomoyo/Kconfig"
diff --git a/security/Kconfig.initmem b/security/Kconfig.initmem
new file mode 100644
index 000000000000..5ac3cf3e7f88
--- /dev/null
+++ b/security/Kconfig.initmem
@@ -0,0 +1,22 @@
+menu "Initialize all memory"
+
+config INIT_ALL_MEMORY
+ bool "Initialize all memory"
+ default n
+ help
+ Enforce memory initialization to mitigate infoleaks and make
+ the control-flow bugs depending on uninitialized values more
+ deterministic.
+
+if INIT_ALL_MEMORY
+
+config INIT_ALL_STACK
+ bool "Initialize all stack"
+ depends on INIT_ALL_MEMORY
+ default y
+ help
+ Initialize uninitialized stack data with a 0xAA pattern.
+ This config option only supports Clang builds at the moment.
+
+endif # INIT_ALL_MEMORY
+endmenu
--
2.21.0.352.gf09ad66450-goog
