On Wed, Dec 12, 2018 at 4:08 AM Ard Biesheuvel <[email protected]> wrote: > > This enables the use of per-task stack canary values if GCC has > support for emitting the stack canary reference relative to the > value of sp_el0, which holds the task struct pointer in the arm64 > kernel. > > The $(eval) extends KBUILD_CFLAGS at the moment the make rule is > applied, which means asm-offsets.o (which we rely on for the offset > value) is built without the arguments, and everything built afterwards > has the options set. > > Signed-off-by: Ard Biesheuvel <[email protected]>
Reviewed-by: Kees Cook <[email protected]> -Kees > --- > v3: add all 3 options to the Kconfig cc-option check, to avoid relying on > implementation defined logic in the compiler regarding which options > need to appear together. > > arch/arm64/Kconfig | 7 +++++++ > arch/arm64/Makefile | 10 ++++++++++ > arch/arm64/include/asm/stackprotector.h | 3 ++- > arch/arm64/kernel/asm-offsets.c | 3 +++ > arch/arm64/kernel/process.c | 2 +- > 5 files changed, 23 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index ea2ab0330e3a..e355946cde97 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -1272,6 +1272,13 @@ config RANDOMIZE_MODULE_REGION_FULL > a limited range that contains the [_stext, _etext] interval of the > core kernel, so branch relocations are always in range. > > +config CC_HAVE_STACKPROTECTOR_SYSREG > + def_bool $(cc-option,-mstack-protector-guard=sysreg > -mstack-protector-guard-reg=sp_el0 -mstack-protector-guard-offset=0) > + > +config STACKPROTECTOR_PER_TASK > + def_bool y > + depends on STACKPROTECTOR && CC_HAVE_STACKPROTECTOR_SYSREG > + > endmenu > > menu "Boot options" > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index 6cb9fc7e9382..79d927542322 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -56,6 +56,16 @@ KBUILD_AFLAGS += $(lseinstr) $(brokengasinst) > KBUILD_CFLAGS += $(call cc-option,-mabi=lp64) > KBUILD_AFLAGS += $(call cc-option,-mabi=lp64) > > +ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y) > +prepare: stack_protector_prepare > +stack_protector_prepare: prepare0 > + $(eval KBUILD_CFLAGS += -mstack-protector-guard=sysreg \ > + -mstack-protector-guard-reg=sp_el0 \ > + -mstack-protector-guard-offset=$(shell \ > + awk '{if ($$2 == "TSK_STACK_CANARY") print $$3;}' \ > + include/generated/asm-offsets.h)) > +endif > + > ifeq ($(CONFIG_CPU_BIG_ENDIAN), y) > KBUILD_CPPFLAGS += -mbig-endian > CHECKFLAGS += -D__AARCH64EB__ > diff --git a/arch/arm64/include/asm/stackprotector.h > b/arch/arm64/include/asm/stackprotector.h > index 58d15be11c4d..5884a2b02827 100644 > --- a/arch/arm64/include/asm/stackprotector.h > +++ b/arch/arm64/include/asm/stackprotector.h > @@ -34,7 +34,8 @@ static __always_inline void boot_init_stack_canary(void) > canary &= CANARY_MASK; > > current->stack_canary = canary; > - __stack_chk_guard = current->stack_canary; > + if (!IS_ENABLED(CONFIG_STACKPROTECTOR_PER_TASK)) > + __stack_chk_guard = current->stack_canary; > } > > #endif /* _ASM_STACKPROTECTOR_H */ > diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c > index 323aeb5f2fe6..65b8afc84466 100644 > --- a/arch/arm64/kernel/asm-offsets.c > +++ b/arch/arm64/kernel/asm-offsets.c > @@ -46,6 +46,9 @@ int main(void) > DEFINE(TSK_TI_TTBR0, offsetof(struct task_struct, > thread_info.ttbr0)); > #endif > DEFINE(TSK_STACK, offsetof(struct task_struct, stack)); > +#ifdef CONFIG_STACKPROTECTOR > + DEFINE(TSK_STACK_CANARY, offsetof(struct task_struct, stack_canary)); > +#endif > BLANK(); > DEFINE(THREAD_CPU_CONTEXT, offsetof(struct task_struct, > thread.cpu_context)); > BLANK(); > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index d9a4c2d6dd8b..8a2d68f04e0d 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -59,7 +59,7 @@ > #include <asm/processor.h> > #include <asm/stacktrace.h> > > -#ifdef CONFIG_STACKPROTECTOR > +#if defined(CONFIG_STACKPROTECTOR) && > !defined(CONFIG_STACKPROTECTOR_PER_TASK) > #include <linux/stackprotector.h> > unsigned long __stack_chk_guard __read_mostly; > EXPORT_SYMBOL(__stack_chk_guard); > -- > 2.19.2 > > s -- Kees Cook
