On Thu, Oct 31, 2019 at 9:47 AM <samitolvanen@xxxxxxxxxx> wrote: > > 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. Inline/out-of-line assembly will also need to be careful not to accidentally overwrite the current task's shadow stack pointer. Without automated checking for that, we'll have to rely on a "gentlemen's promise" for code reviewers, though we'd likely hit such a regression with Android+mainline. Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx> > --- > arch/arm64/Makefile | 4 ++++ > 1 file changed, 4 insertions(+) > > 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__ > -- > 2.24.0.rc0.303.g954a862665-goog > -- Thanks, ~Nick Desaulniers
