[PATCH 12/18] arm64: reserve x18 only with Shadow Call Stack

Sami Tolvanen
2019-10-18T16:15:52Z

Only reserve x18 with CONFIG_SHADOW_CALL_STACK. Note that all external
kernel modules must also have x18 reserved if the kernel uses SCS.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
arch/arm64/Makefile | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 1c7b276bc7c5..ef76101201b2 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -55,7 +55,7 @@ endif

KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) $(brokengasinst) \
$(compat_vdso) $(cc_has_k_constraint)
-KBUILD_CFLAGS += -fno-asynchronous-unwind-tables -ffixed-x18
+KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
KBUILD_CFLAGS += $(call cc-disable-warning, psabi)
KBUILD_AFLAGS += $(lseinstr) $(brokengasinst) $(compat_vdso)

@@ -72,6 +72,10 @@ stack_protector_prepare: prepare0
include/generated/asm-offsets.h))
endif

+ifeq ($(CONFIG_SHADOW_CALL_STACK), y)
+KBUILD_CFLAGS += -ffixed-x18
+endif
+
ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
KBUILD_CPPFLAGS += -mbig-endian
CHECKFLAGS += -D__AARCH64EB__
--
2.23.0.866.gb869b98d4c-goog