On Wed, 3 Mar 2021 at 18:10, Julien Thierry <jthie...@redhat.com> wrote: > > From: Raphael Gault <raphael.ga...@arm.com> > > Add build option to run stack validation at compile time. > > When requiring stack validation, jump tables are disabled as it > simplifies objtool analysis (without having to introduce unreliable > artifacs). In local testing, this does not appear to significaly > affect final binary size nor system performance. > > Signed-off-by: Raphael Gault <raphael.ga...@arm.com> > Signed-off-by: Julien Thierry <jthie...@redhat.com> > --- > arch/arm64/Kconfig | 1 + > arch/arm64/Makefile | 4 ++++ > 2 files changed, 5 insertions(+) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 1f212b47a48a..928323c03318 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -187,6 +187,7 @@ config ARM64 > select MMU_GATHER_RCU_TABLE_FREE > select HAVE_RSEQ > select HAVE_STACKPROTECTOR > + select HAVE_STACK_VALIDATION > select HAVE_SYSCALL_TRACEPOINTS > select HAVE_KPROBES > select HAVE_KRETPROBES > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index 5b84aec31ed3..b819fb2e8eda 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -136,6 +136,10 @@ ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_REGS),y) > CC_FLAGS_FTRACE := -fpatchable-function-entry=2 > endif > > +ifeq ($(CONFIG_STACK_VALIDATION),y) > +KBUILD_CFLAGS += -fno-jump-tables > +endif > +
This is a bit misleading: the Kconfig option in question is selected automatically in all cases, so jump tables are always disabled. However, I think disabling jump tables make sense anyway, at least when building the relocatable kernel for KASLR: we currently don't use -fpic/fpie in that case when building the vmlinux objects (because we don't want/need GOT tables), and so jump tables are emitted using absolute addresses, which induce some space overhead in the image. (24 bytes of RELA data per absolute address) ... unless I am missing something, and jump tables can/will be emitted as relative, even when not compiling in PIC mode? > # Default value > head-y := arch/arm64/kernel/head.o > > -- > 2.25.4 >
