arm64: Enable KCSAN

This patch enables KCSAN for arm64, with updates to build rules
to not use KCSAN for several incompatible compilation units.

Recent GCC version(at least GCC10) made outline-atomics as the
default option(unlike Clang), which will cause linker errors
for kernel/kcsan/core.o. Disables the out-of-line atomics by
no-outline-atomics to fix the linker errors.

Meanwhile, as Mark said[1], some latent issues are needed to be
fixed which isn't just a KCSAN problem, we make the KCSAN depends
on EXPERT for now.

Tested selftest and kcsan_test(built with GCC11 and Clang 13),
and all passed.

[1] https://lkml.kernel.org/r/YadiUPpJ0gADbiHQ@FVFF77S0Q05N

Acked-by: Marco Elver <elver@google.com> # kernel/kcsan
Tested-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/20211211131734.126874-1-wangkefeng.wang@huawei.com
[catalin.marinas@arm.com: added comment to justify EXPERT]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/Kconfig

@@ -150,6 +150,8 @@ config ARM64
 	select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
 	select HAVE_ARCH_KASAN_SW_TAGS if HAVE_ARCH_KASAN
 	select HAVE_ARCH_KASAN_HW_TAGS if (HAVE_ARCH_KASAN && ARM64_MTE)
+	# Some instrumentation may be unsound, hence EXPERT
+	select HAVE_ARCH_KCSAN if EXPERT
 	select HAVE_ARCH_KFENCE
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS

arch/arm64/kernel/vdso/Makefile

@@ -32,6 +32,7 @@ ccflags-y += -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
 CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS) $(GCC_PLUGINS_CFLAGS) \
 				$(CC_FLAGS_LTO)
 KASAN_SANITIZE			:= n
+KCSAN_SANITIZE			:= n
 UBSAN_SANITIZE			:= n
 OBJECT_FILES_NON_STANDARD	:= y
 KCOV_INSTRUMENT			:= n

arch/arm64/kvm/hyp/nvhe/Makefile

@@ -89,6 +89,7 @@ KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS) $(CC_FLAGS_CFI)
 # cause crashes. Just disable it.
 GCOV_PROFILE	:= n
 KASAN_SANITIZE	:= n
+KCSAN_SANITIZE	:= n
 UBSAN_SANITIZE	:= n
 KCOV_INSTRUMENT	:= n
 

kernel/kcsan/Makefile

@@ -8,6 +8,7 @@ CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
 
 CFLAGS_core.o := $(call cc-option,-fno-conserve-stack) \
+	$(call cc-option,-mno-outline-atomics) \
 	-fno-stack-protector -DDISABLE_BRANCH_PROFILING
 
 obj-y := core.o debugfs.o report.o