ARM: 9028/1: disable KASAN in call stack capturing routines

KASAN uses the routines in stacktrace.c to capture the call stack each
time memory gets allocated or freed. Some of these routines are also
used to log CPU and memory context when exceptions are taken, and so
in some cases, memory accesses may be made that are not strictly in
line with the KASAN constraints, and may therefore trigger false KASAN
positives.

So follow the example set by other architectures, and simply disable
KASAN instrumentation for these routines.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/kernel/Makefile

@@ -21,6 +21,9 @@ obj-y		:= elf.o entry-common.o irq.o opcodes.o \
 		   setup.o signal.o sigreturn_codes.o \
 		   stacktrace.o sys_arm.o time.o traps.o
 
+KASAN_SANITIZE_stacktrace.o := n
+KASAN_SANITIZE_traps.o := n
+
 ifneq ($(CONFIG_ARM_UNWIND),y)
 obj-$(CONFIG_FRAME_POINTER)	+= return_address.o
 endif