diff mbox series

[v4,12/17] arm64: reserve x18 from general allocation with SCS

Message ID 20191101221150.116536-13-samitolvanen@google.com (mailing list archive)
State New, archived
Headers show
Series [v4,01/17] arm64: mm: avoid x18 in idmap_kpti_install_ng_mappings | expand

Commit Message

Sami Tolvanen Nov. 1, 2019, 10:11 p.m. UTC 
Reserve the x18 register from general allocation when SCS is enabled,
because the compiler uses the register to store the current task's
shadow stack pointer. Note that all external kernel modules must also be
compiled with -ffixed-x18 if the kernel has SCS enabled.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 arch/arm64/Makefile | 4 ++++
 1 file changed, 4 insertions(+)
diff mbox series

Patch

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 2c0238ce0551..ef76101201b2 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -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__