| Message ID | 202006221201.3641ED037E@keescook (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: Provide way to actually disable stack protector | expand |
On Tue, Jun 23, 2020 at 4:02 AM Kees Cook <keescook@chromium.org> wrote: > > Some builds of GCC enable stack protector by default. Simply removing > the arguments is not sufficient to disable stack protector, as the stack > protector for those GCC builds must be explicitly disabled. (Removing the > arguments is left as-is just to be sure there are no ordering problems. If > -fno-stack-protector ended up _before_ -fstack-protector, it would not > disable it: GCC uses whichever -f... comes last on the command line.) > > Fixes: 20355e5f73a7 ("x86/entry: Exclude low level entry code from sanitizing") > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > Makefile | 4 +++- > arch/Kconfig | 3 --- > arch/arm/boot/compressed/Makefile | 4 ++-- > arch/x86/entry/Makefile | 3 +++ > 4 files changed, 8 insertions(+), 6 deletions(-) > > diff --git a/Makefile b/Makefile > index ac2c61c37a73..b46e91bf0b0e 100644 > --- a/Makefile > +++ b/Makefile > @@ -762,7 +762,9 @@ ifneq ($(CONFIG_FRAME_WARN),0) > KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN) > endif > > -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector > +DISABLE_STACKPROTECTOR := $(call cc-option,-fno-stack-protector) > +export DISABLE_STACKPROTECTOR > +stackp-flags-y := $(DISABLE_STACKPROTECTOR) > stackp-flags-$(CONFIG_STACKPROTECTOR) := -fstack-protector > stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG) := -fstack-protector-strong > > diff --git a/arch/Kconfig b/arch/Kconfig > index 8cc35dc556c7..1ea61290900a 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR > An arch should select this symbol if: > - it has implemented a stack canary (e.g. __stack_chk_guard) > > -config CC_HAS_STACKPROTECTOR_NONE > - def_bool $(cc-option,-fno-stack-protector) > - > config STACKPROTECTOR > bool "Stack Protector buffer overflow detection" > depends on HAVE_STACKPROTECTOR > diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile > index 00602a6fba04..3693bac525d2 100644 > --- a/arch/arm/boot/compressed/Makefile > +++ b/arch/arm/boot/compressed/Makefile > @@ -84,9 +84,9 @@ endif > > # -fstack-protector-strong triggers protection checks in this code, > # but it is being used too early to link to meaningful stack_chk logic. > -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector > $(foreach o, $(libfdt_objs) atags_to_fdt.o, \ > - $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y))) > + $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt \ > + $(DISABLE_STACKPROTECTOR))) > > # These were previously generated C files. When you are building the kernel > # with O=, make sure to remove the stale files in the output tree. Otherwise, > diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile > index b7a5790d8d63..79902decc3d1 100644 > --- a/arch/x86/entry/Makefile > +++ b/arch/x86/entry/Makefile > @@ -10,6 +10,9 @@ KCOV_INSTRUMENT := n > CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong > CFLAGS_REMOVE_syscall_32.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong > CFLAGS_REMOVE_syscall_64.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong > +CFLAGS_common.o += $(DISABLE_STACKPROTECTOR) > +CFLAGS_syscall_32.o += $(DISABLE_STACKPROTECTOR) > +CFLAGS_syscall_64.o += $(DISABLE_STACKPROTECTOR) There is one more c file in this directory. Is it OK to not patch syscall_x32.c ? > > CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,) > CFLAGS_syscall_32.o += $(call cc-option,-Wno-override-init,) This patch is ugly. I'd rather want to fix this by one-liner. diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile index b7a5790d8d63..0d41eb91aaea 100644 --- a/arch/x86/entry/Makefile +++ b/arch/x86/entry/Makefile @@ -11,6 +11,8 @@ CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector- CFLAGS_REMOVE_syscall_32.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong CFLAGS_REMOVE_syscall_64.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong +ccflags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) += -fno-stack-protector + CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,) CFLAGS_syscall_32.o += $(call cc-option,-Wno-override-init,) obj-y := entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
On Tue, Jun 23, 2020 at 11:33:53AM +0900, Masahiro Yamada wrote: > On Tue, Jun 23, 2020 at 4:02 AM Kees Cook <keescook@chromium.org> wrote: > > > > Some builds of GCC enable stack protector by default. Simply removing > > the arguments is not sufficient to disable stack protector, as the stack > > protector for those GCC builds must be explicitly disabled. (Removing the > > arguments is left as-is just to be sure there are no ordering problems. If > > -fno-stack-protector ended up _before_ -fstack-protector, it would not > > disable it: GCC uses whichever -f... comes last on the command line.) > > > > Fixes: 20355e5f73a7 ("x86/entry: Exclude low level entry code from sanitizing") > > Signed-off-by: Kees Cook <keescook@chromium.org> > > --- > > Makefile | 4 +++- > > arch/Kconfig | 3 --- > > arch/arm/boot/compressed/Makefile | 4 ++-- > > arch/x86/entry/Makefile | 3 +++ > > 4 files changed, 8 insertions(+), 6 deletions(-) > > > > diff --git a/Makefile b/Makefile > > index ac2c61c37a73..b46e91bf0b0e 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -762,7 +762,9 @@ ifneq ($(CONFIG_FRAME_WARN),0) > > KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN) > > endif > > > > -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector > > +DISABLE_STACKPROTECTOR := $(call cc-option,-fno-stack-protector) > > +export DISABLE_STACKPROTECTOR > > +stackp-flags-y := $(DISABLE_STACKPROTECTOR) > > stackp-flags-$(CONFIG_STACKPROTECTOR) := -fstack-protector > > stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG) := -fstack-protector-strong > > > > diff --git a/arch/Kconfig b/arch/Kconfig > > index 8cc35dc556c7..1ea61290900a 100644 > > --- a/arch/Kconfig > > +++ b/arch/Kconfig > > @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR > > An arch should select this symbol if: > > - it has implemented a stack canary (e.g. __stack_chk_guard) > > > > -config CC_HAS_STACKPROTECTOR_NONE > > - def_bool $(cc-option,-fno-stack-protector) > > - > > config STACKPROTECTOR > > bool "Stack Protector buffer overflow detection" > > depends on HAVE_STACKPROTECTOR > > diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile > > index 00602a6fba04..3693bac525d2 100644 > > --- a/arch/arm/boot/compressed/Makefile > > +++ b/arch/arm/boot/compressed/Makefile > > @@ -84,9 +84,9 @@ endif > > > > # -fstack-protector-strong triggers protection checks in this code, > > # but it is being used too early to link to meaningful stack_chk logic. > > -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector > > $(foreach o, $(libfdt_objs) atags_to_fdt.o, \ > > - $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y))) > > + $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt \ > > + $(DISABLE_STACKPROTECTOR))) > > > > # These were previously generated C files. When you are building the kernel > > # with O=, make sure to remove the stale files in the output tree. Otherwise, > > diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile > > index b7a5790d8d63..79902decc3d1 100644 > > --- a/arch/x86/entry/Makefile > > +++ b/arch/x86/entry/Makefile > > @@ -10,6 +10,9 @@ KCOV_INSTRUMENT := n > > CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong > > CFLAGS_REMOVE_syscall_32.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong > > CFLAGS_REMOVE_syscall_64.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong > > +CFLAGS_common.o += $(DISABLE_STACKPROTECTOR) > > +CFLAGS_syscall_32.o += $(DISABLE_STACKPROTECTOR) > > +CFLAGS_syscall_64.o += $(DISABLE_STACKPROTECTOR) > > There is one more c file in this directory. > > Is it OK to not patch syscall_x32.c ? Good question. Peter? (It seems all the syscall_*.c files are just a table, not code -- why do they need any instrumentation changes?) > > > > > > CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,) > > CFLAGS_syscall_32.o += $(call cc-option,-Wno-override-init,) > > > > > This patch is ugly. > > I'd rather want to fix this by one-liner. Why not a global export to assist? This isn't the only place it's needed (see the arm64 chunk...) > > > > > diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile > index b7a5790d8d63..0d41eb91aaea 100644 > --- a/arch/x86/entry/Makefile > +++ b/arch/x86/entry/Makefile > @@ -11,6 +11,8 @@ CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE) > -fstack-protector -fstack-protector- > CFLAGS_REMOVE_syscall_32.o = $(CC_FLAGS_FTRACE) -fstack-protector > -fstack-protector-strong > CFLAGS_REMOVE_syscall_64.o = $(CC_FLAGS_FTRACE) -fstack-protector > -fstack-protector-strong > > +ccflags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) += -fno-stack-protector > + Order matters here -- when is ccflags-y applied? > CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,) > CFLAGS_syscall_32.o += $(call cc-option,-Wno-override-init,) > obj-y := entry_$(BITS).o thunk_$(BITS).o > syscall_$(BITS).o > > > > > -- > Best Regards > Masahiro Yamada
On Tue, Jun 23, 2020 at 2:37 PM Kees Cook <keescook@chromium.org> wrote: > > On Tue, Jun 23, 2020 at 11:33:53AM +0900, Masahiro Yamada wrote: > > On Tue, Jun 23, 2020 at 4:02 AM Kees Cook <keescook@chromium.org> wrote: > > > > > > Some builds of GCC enable stack protector by default. Simply removing > > > the arguments is not sufficient to disable stack protector, as the stack > > > protector for those GCC builds must be explicitly disabled. (Removing the > > > arguments is left as-is just to be sure there are no ordering problems. If > > > -fno-stack-protector ended up _before_ -fstack-protector, it would not > > > disable it: GCC uses whichever -f... comes last on the command line.) > > > > > > Fixes: 20355e5f73a7 ("x86/entry: Exclude low level entry code from sanitizing") > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > --- > > > Makefile | 4 +++- > > > arch/Kconfig | 3 --- > > > arch/arm/boot/compressed/Makefile | 4 ++-- > > > arch/x86/entry/Makefile | 3 +++ > > > 4 files changed, 8 insertions(+), 6 deletions(-) > > > > > > diff --git a/Makefile b/Makefile > > > index ac2c61c37a73..b46e91bf0b0e 100644 > > > --- a/Makefile > > > +++ b/Makefile > > > @@ -762,7 +762,9 @@ ifneq ($(CONFIG_FRAME_WARN),0) > > > KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN) > > > endif > > > > > > -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector > > > +DISABLE_STACKPROTECTOR := $(call cc-option,-fno-stack-protector) > > > +export DISABLE_STACKPROTECTOR > > > +stackp-flags-y := $(DISABLE_STACKPROTECTOR) > > > stackp-flags-$(CONFIG_STACKPROTECTOR) := -fstack-protector > > > stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG) := -fstack-protector-strong > > > > > > diff --git a/arch/Kconfig b/arch/Kconfig > > > index 8cc35dc556c7..1ea61290900a 100644 > > > --- a/arch/Kconfig > > > +++ b/arch/Kconfig > > > @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR > > > An arch should select this symbol if: > > > - it has implemented a stack canary (e.g. __stack_chk_guard) > > > > > > -config CC_HAS_STACKPROTECTOR_NONE > > > - def_bool $(cc-option,-fno-stack-protector) > > > - > > > config STACKPROTECTOR > > > bool "Stack Protector buffer overflow detection" > > > depends on HAVE_STACKPROTECTOR > > > diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile > > > index 00602a6fba04..3693bac525d2 100644 > > > --- a/arch/arm/boot/compressed/Makefile > > > +++ b/arch/arm/boot/compressed/Makefile > > > @@ -84,9 +84,9 @@ endif > > > > > > # -fstack-protector-strong triggers protection checks in this code, > > > # but it is being used too early to link to meaningful stack_chk logic. > > > -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector > > > $(foreach o, $(libfdt_objs) atags_to_fdt.o, \ > > > - $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y))) > > > + $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt \ > > > + $(DISABLE_STACKPROTECTOR))) > > > > > > # These were previously generated C files. When you are building the kernel > > > # with O=, make sure to remove the stale files in the output tree. Otherwise, > > > diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile > > > index b7a5790d8d63..79902decc3d1 100644 > > > --- a/arch/x86/entry/Makefile > > > +++ b/arch/x86/entry/Makefile > > > @@ -10,6 +10,9 @@ KCOV_INSTRUMENT := n > > > CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong > > > CFLAGS_REMOVE_syscall_32.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong > > > CFLAGS_REMOVE_syscall_64.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong > > > +CFLAGS_common.o += $(DISABLE_STACKPROTECTOR) > > > +CFLAGS_syscall_32.o += $(DISABLE_STACKPROTECTOR) > > > +CFLAGS_syscall_64.o += $(DISABLE_STACKPROTECTOR) > > > > There is one more c file in this directory. > > > > Is it OK to not patch syscall_x32.c ? > > Good question. Peter? (It seems all the syscall_*.c files are just a > table, not code -- why do they need any instrumentation changes?) > > > > > > > > > > > CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,) > > > CFLAGS_syscall_32.o += $(call cc-option,-Wno-override-init,) > > > > > > > > > > This patch is ugly. > > > > I'd rather want to fix this by one-liner. > > Why not a global export to assist? This isn't the only place it's needed > (see the arm64 chunk...) Is it useful when we know DISABLE_STACKPROTECTOR = -fno-stack-protector ? I'd rather want to apply this patch https://patchwork.kernel.org/patch/11628493/ and hard-code -fno-stack-protector where necessary. > > > > > > > > > > > diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile > > index b7a5790d8d63..0d41eb91aaea 100644 > > --- a/arch/x86/entry/Makefile > > +++ b/arch/x86/entry/Makefile > > @@ -11,6 +11,8 @@ CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE) > > -fstack-protector -fstack-protector- > > CFLAGS_REMOVE_syscall_32.o = $(CC_FLAGS_FTRACE) -fstack-protector > > -fstack-protector-strong > > CFLAGS_REMOVE_syscall_64.o = $(CC_FLAGS_FTRACE) -fstack-protector > > -fstack-protector-strong > > > > +ccflags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) += -fno-stack-protector > > + > > Order matters here -- when is ccflags-y applied? cc-flags-y comes after KBUILD_CFLAGS so that -fno-stack-protector can negate -fstack-protector(-strong) > > > CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,) > > CFLAGS_syscall_32.o += $(call cc-option,-Wno-override-init,) > > obj-y := entry_$(BITS).o thunk_$(BITS).o > > syscall_$(BITS).o > > > > > > > > > > -- > > Best Regards > > Masahiro Yamada > > -- > Kees Cook
On Sat, Jun 27, 2020 at 04:04:33AM +0900, Masahiro Yamada wrote: > On Tue, Jun 23, 2020 at 2:37 PM Kees Cook <keescook@chromium.org> wrote: > > > > On Tue, Jun 23, 2020 at 11:33:53AM +0900, Masahiro Yamada wrote: > > > Is it OK to not patch syscall_x32.c ? > > > > Good question. Peter? (It seems all the syscall_*.c files are just a > > table, not code -- why do they need any instrumentation changes?) I'd still like to know the answer to this one... > Is it useful when we know > DISABLE_STACKPROTECTOR = -fno-stack-protector ? I'm fine with that. My point was the using _REMOVE isn't going to work for some compiler builds. > I'd rather want to apply this patch > https://patchwork.kernel.org/patch/11628493/ > and hard-code -fno-stack-protector where necessary. That's fine. I will send a separate fix for arch/x86/entry/Makefile. > cc-flags-y comes after KBUILD_CFLAGS > so that -fno-stack-protector can negate -fstack-protector(-strong) Okay, good.
diff --git a/Makefile b/Makefile index ac2c61c37a73..b46e91bf0b0e 100644 --- a/Makefile +++ b/Makefile @@ -762,7 +762,9 @@ ifneq ($(CONFIG_FRAME_WARN),0) KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN) endif -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector +DISABLE_STACKPROTECTOR := $(call cc-option,-fno-stack-protector) +export DISABLE_STACKPROTECTOR +stackp-flags-y := $(DISABLE_STACKPROTECTOR) stackp-flags-$(CONFIG_STACKPROTECTOR) := -fstack-protector stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG) := -fstack-protector-strong diff --git a/arch/Kconfig b/arch/Kconfig index 8cc35dc556c7..1ea61290900a 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR An arch should select this symbol if: - it has implemented a stack canary (e.g. __stack_chk_guard) -config CC_HAS_STACKPROTECTOR_NONE - def_bool $(cc-option,-fno-stack-protector) - config STACKPROTECTOR bool "Stack Protector buffer overflow detection" depends on HAVE_STACKPROTECTOR diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile index 00602a6fba04..3693bac525d2 100644 --- a/arch/arm/boot/compressed/Makefile +++ b/arch/arm/boot/compressed/Makefile @@ -84,9 +84,9 @@ endif # -fstack-protector-strong triggers protection checks in this code, # but it is being used too early to link to meaningful stack_chk logic. -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector $(foreach o, $(libfdt_objs) atags_to_fdt.o, \ - $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y))) + $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt \ + $(DISABLE_STACKPROTECTOR))) # These were previously generated C files. When you are building the kernel # with O=, make sure to remove the stale files in the output tree. Otherwise, diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile index b7a5790d8d63..79902decc3d1 100644 --- a/arch/x86/entry/Makefile +++ b/arch/x86/entry/Makefile @@ -10,6 +10,9 @@ KCOV_INSTRUMENT := n CFLAGS_REMOVE_common.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong CFLAGS_REMOVE_syscall_32.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong CFLAGS_REMOVE_syscall_64.o = $(CC_FLAGS_FTRACE) -fstack-protector -fstack-protector-strong +CFLAGS_common.o += $(DISABLE_STACKPROTECTOR) +CFLAGS_syscall_32.o += $(DISABLE_STACKPROTECTOR) +CFLAGS_syscall_64.o += $(DISABLE_STACKPROTECTOR) CFLAGS_syscall_64.o += $(call cc-option,-Wno-override-init,) CFLAGS_syscall_32.o += $(call cc-option,-Wno-override-init,)
Some builds of GCC enable stack protector by default. Simply removing the arguments is not sufficient to disable stack protector, as the stack protector for those GCC builds must be explicitly disabled. (Removing the arguments is left as-is just to be sure there are no ordering problems. If -fno-stack-protector ended up _before_ -fstack-protector, it would not disable it: GCC uses whichever -f... comes last on the command line.) Fixes: 20355e5f73a7 ("x86/entry: Exclude low level entry code from sanitizing") Signed-off-by: Kees Cook <keescook@chromium.org> --- Makefile | 4 +++- arch/Kconfig | 3 --- arch/arm/boot/compressed/Makefile | 4 ++-- arch/x86/entry/Makefile | 3 +++ 4 files changed, 8 insertions(+), 6 deletions(-)