On Thu, Apr 11, 2019 at 8:01 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > 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@xxxxxxxxxx> > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> Tested-by: Alexander Potapenko <glider@xxxxxxxxxx> > --- > Makefile | 5 +++++ > security/Kconfig.hardening | 15 ++++++++++++++- > 2 files changed, 19 insertions(+), 1 deletion(-) > > 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 3dd7a28c3822..5dd61770d3f0 100644 > --- a/security/Kconfig.hardening > +++ b/security/Kconfig.hardening > @@ -18,9 +18,12 @@ 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" > - depends on GCC_PLUGINS > + depends on CC_HAS_AUTO_VAR_INIT || GCC_PLUGINS > default INIT_STACK_NONE > help > This option enables initialization of stack variables at > @@ -76,6 +79,16 @@ 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 > -- > 2.17.1 > -- 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
