On Thu, Apr 11, 2019 at 1:16 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > CONFIG_INIT_STACK_ALL turns on stack initialization based on > -ftrivial-auto-var-init in Clang builds and on > -fplugin-arg-structleak_plugin-byref-all in GCC builds. Is CONFIG_INIT_STACK_ALL wired up to GCC plugin in any way? I could not understand it from the code. > > -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 when selected. > > Developers have the possibility to opt-out of this feature on a > per-variable basis by using __attribute__((uninitialized)). > > Co-developed-by: Alexander Potapenko <glider@xxxxxxxxxx> > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > Makefile | 5 +++++ > security/Kconfig.hardening | 14 ++++++++++++++ > 2 files changed, 19 insertions(+) > > 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 9942d9869864..d744e20140b4 100644 > --- a/security/Kconfig.hardening > +++ b/security/Kconfig.hardening > @@ -19,9 +19,13 @@ 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" > depends on CC_HAS_AUTO_VAR_INIT || GCC_PLUGINS > + default INIT_STACK_ALL if CC_HAS_AUTO_VAR_INIT Why should this be enabled by default? Ins't it a performance regression since it inserts instructions in function prologue? -- Best Regards Masahiro Yamada
