On Thu, Mar 7, 2019 at 7:37 PM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > On Thu, Mar 7, 2019 at 5:35 AM Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > > > 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 > > Hopefully the disagreements there about "defining a new dialect of > C++" don't apply to us in the kernel. We'd like to have this feature; > our dialect of C is already quite far from what ISO has specified, > both through the explicit use of `-f` compiler flags and use of most > GNU C extensions. We already have our own dialect of C for the > kernel, it's too late for that. But maybe I should go bikeshed in > cfe-dev... > > Thanks for this patch. I'll take a closer look once Kees' feedback > has been addressed. I've sent out the updated version. > > 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 > > > > > -- > Thanks, > ~Nick Desaulniers -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Halimah DeLaine Prado Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg
