From f19fbd5ed642dc31c809596412dab1ed56f2f156 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Fri, 26 Jan 2018 12:46:47 +0100 Subject: s390: introduce execute-trampolines for branches 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 --- arch/s390/Makefile | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'arch/s390/Makefile') diff --git a/arch/s390/Makefile b/arch/s390/Makefile index fd691c4ff89e..2ced3239cb84 100644 --- a/arch/s390/Makefile +++ b/arch/s390/Makefile @@ -78,6 +78,16 @@ ifeq ($(call cc-option-yn,-mwarn-dynamicstack),y) cflags-$(CONFIG_WARN_DYNAMIC_STACK) += -mwarn-dynamicstack endif +ifdef CONFIG_EXPOLINE + ifeq ($(call cc-option-yn,$(CC_FLAGS_MARCH) -mindirect-branch=thunk),y) + CC_FLAGS_EXPOLINE := -mindirect-branch=thunk + CC_FLAGS_EXPOLINE += -mfunction-return=thunk + CC_FLAGS_EXPOLINE += -mindirect-branch-table + export CC_FLAGS_EXPOLINE + cflags-y += $(CC_FLAGS_EXPOLINE) + endif +endif + ifdef CONFIG_FUNCTION_TRACER # make use of hotpatch feature if the compiler supports it cc_hotpatch := -mhotpatch=0,3 -- cgit v1.2.3-59-g8ed1b