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Commit 0a1213fa authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Will Deacon
Browse files

arm64: enable per-task stack canaries 



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.

Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 4ab21506

arch/arm64/Kconfig

+7 −0
Original line number Diff line number Diff line
@@ -1344,6 +1344,13 @@ 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"

arch/arm64/Makefile

+10 −0
Original line number Diff line number Diff line
@@ -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__

arch/arm64/include/asm/stackprotector.h

+2 −1
Original line number Diff line number Diff line
@@ -34,6 +34,7 @@ static __always_inline void boot_init_stack_canary(void) 
	canary &= CANARY_MASK;



	current->stack_canary = canary;

	if (!IS_ENABLED(CONFIG_STACKPROTECTOR_PER_TASK))

		__stack_chk_guard = current->stack_canary;

}

arch/arm64/kernel/asm-offsets.c

+3 −0
Original line number Diff line number Diff line
@@ -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();

arch/arm64/kernel/process.c

+1 −1
Original line number Diff line number Diff line
@@ -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);