On Tue, Apr 9, 2019 at 2:04 AM Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > CONFIG_INIT_ALL_MEMORY is going to be an umbrella config for options > that force heap and stack initialization. > The rationale behind doing so is to reduce the severity of bugs caused > by using uninitialized memory. > > CONFIG_INIT_ALL_STACK turns on stack initialization based on > -ftrivial-auto-var-init in Clang builds and on > -fplugin-arg-structleak_plugin-byref-all in GCC builds. > > -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-variable basis by using __attribute__((uninitialized)). > > For GCC builds, CONFIG_INIT_ALL_STACK is simply wired up to > CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL. No opt-out is possible at the > moment. > > 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 > Cc: kernel-hardening@xxxxxxxxxxxxxxxxxx > --- > v2: > - addressed Kees Cook's comments: added GCC support > v3: addressed Masahiro Yamada's comments: > - dropped per-file opt-out mechanism > - fixed GCC_PLUGINS dependencies > --- > Makefile | 3 ++- > scripts/Makefile.initmem | 10 ++++++++++ > security/Kconfig | 1 + > security/Kconfig.initmem | 29 +++++++++++++++++++++++++++++ > 4 files changed, 42 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..a6253d78fe35 > --- /dev/null > +++ b/scripts/Makefile.initmem > @@ -0,0 +1,10 @@ > +ifdef CONFIG_INIT_ALL_STACK > + > +# 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_CC_HAS_AUTO_VAR_INIT > + CFLAGS_INITMEM := -ftrivial-auto-var-init=pattern > +endif > + > +endif Now that you dropped per-file control, why is this necessary? Also, CFLAGS_INITMEM is not wired up to anything, so this patch has no effect. I think you can add the following to top Makefile, and that's it. ifdef CONFIG_AUTO_VAR_INIT KBUILD_CFLAGS += -ftrivial-auto-var-init=pattern endif > 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..5e49a55382ad > --- /dev/null > +++ b/security/Kconfig.initmem > @@ -0,0 +1,29 @@ > +menu "Initialize all memory" > + > +config CC_HAS_AUTO_VAR_INIT > + def_bool $(cc-option,-ftrivial-auto-var-init=pattern) > + > +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 > + depends on CC_HAS_AUTO_VAR_INIT || (HAVE_GCC_PLUGINS && PLUGIN_HOSTCC != "") > + select GCC_PLUGINS if !CC_HAS_AUTO_VAR_INIT > + select GCC_PLUGIN_STRUCTLEAK if !CC_HAS_AUTO_VAR_INIT > + select GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if !CC_HAS_AUTO_VAR_INIT > + default y > + help > + Initialize uninitialized stack data with a fixed pattern > + (0x00 in GCC, 0xAA in Clang). > + I am not sure about the benefit of these umbrella CONFIGs since these make 'depends on' and 'select' complicated. I will leave it to Kees, though. > +endif # INIT_ALL_MEMORY > +endmenu > -- > 2.21.0.392.gf8f6787159e-goog > -- Best Regards Masahiro Yamada
