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arm64: enable per-task stack canaries

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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: Kees Cook <keescook@chromium.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Ard Biesheuvel 2018-12-12 13:08:44 +01:00 committed by Will Deacon
parent 4ab2150615
commit 0a1213fa74
5 changed files with 23 additions and 2 deletions
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7
arch/arm64/Kconfig
View File

@ -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"

10
arch/arm64/Makefile
View File

@ -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__

3
arch/arm64/include/asm/stackprotector.h
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@ -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 */

3
arch/arm64/kernel/asm-offsets.c
View File

@ -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();

2
arch/arm64/kernel/process.c
View File

@ -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);