From d6e925eca0f971476baf4def542580b37e0df80d Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Fri, 27 Apr 2018 07:36:53 +0200 Subject: s390: introduce execute-trampolines for branches [ Upstream commit f19fbd5ed642dc31c809596412dab1ed56f2f156 ] Add CONFIG_EXPOLINE to enable the use of the new -mindirect-branch= and -mfunction_return= compiler options to create a kernel fortified against the specte v2 attack. With CONFIG_EXPOLINE=y all indirect branches will be issued with an execute type instruction. For z10 or newer the EXRL instruction will be used, for older machines the EX instruction. The typical indirect call basr %r14,%r1 is replaced with a PC relative call to a new thunk brasl %r14,__s390x_indirect_jump_r1 The thunk contains the EXRL/EX instruction to the indirect branch __s390x_indirect_jump_r1: exrl 0,0f j . 0: br %r1 The detour via the execute type instruction has a performance impact. To get rid of the detour the new kernel parameter "nospectre_v2" and "spectre_v2=[on,off,auto]" can be used. If the parameter is specified the kernel and module code will be patched at runtime. Signed-off-by: Martin Schwidefsky Signed-off-by: Greg Kroah-Hartman --- arch/s390/kernel/Makefile | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/s390/kernel/Makefile') diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile index a4c95c847905..9c9cf5331d6f 100644 --- a/arch/s390/kernel/Makefile +++ b/arch/s390/kernel/Makefile @@ -48,6 +48,9 @@ obj-y += entry.o reipl.o relocate_kernel.o alternative.o extra-y += head.o head64.o vmlinux.lds +obj-$(CONFIG_EXPOLINE) += nospec-branch.o +CFLAGS_REMOVE_expoline.o += $(CC_FLAGS_EXPOLINE) + obj-$(CONFIG_MODULES) += s390_ksyms.o module.o obj-$(CONFIG_SMP) += smp.o obj-$(CONFIG_SCHED_BOOK) += topology.o -- cgit v1.2.3