From dee55c07b037429a8554e77bf1eff51bba9e39e1 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Thu, 28 Jan 2021 15:52:19 -0600 Subject: [PATCH] x86/build: Disable CET instrumentation in the kernel commit 20bf2b378729c4a0366a53e2018a0b70ace94bcd upstream. With retpolines disabled, some configurations of GCC, and specifically the GCC versions 9 and 10 in Ubuntu will add Intel CET instrumentation to the kernel by default. That breaks certain tracing scenarios by adding a superfluous ENDBR64 instruction before the fentry call, for functions which can be called indirectly. CET instrumentation isn't currently necessary in the kernel, as CET is only supported in user space. Disable it unconditionally and move it into the x86's Makefile as CET/CFI... enablement should be a per-arch decision anyway. [ bp: Massage and extend commit message. ] Fixes: 29be86d7f9cb ("kbuild: add -fcf-protection=none when using retpoline flags") Reported-by: Nikolay Borisov Signed-off-by: Josh Poimboeuf Signed-off-by: Borislav Petkov Reviewed-by: Nikolay Borisov Tested-by: Nikolay Borisov Cc: Cc: Seth Forshee Cc: Masahiro Yamada Link: https://lkml.kernel.org/r/20210128215219.6kct3h2eiustncws@treble Signed-off-by: Greg Kroah-Hartman --- Makefile | 6 ------ arch/x86/Makefile | 3 +++ 2 files changed, 3 insertions(+), 6 deletions(-) diff --git a/Makefile b/Makefile index e4c6b6e62edb9..9e126dc1bc404 100644 --- a/Makefile +++ b/Makefile @@ -830,12 +830,6 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=strict-prototypes) # Prohibit date/time macros, which would make the build non-deterministic KBUILD_CFLAGS += $(call cc-option,-Werror=date-time) -# ensure -fcf-protection is disabled when using retpoline as it is -# incompatible with -mindirect-branch=thunk-extern -ifdef CONFIG_RETPOLINE -KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none) -endif - # use the deterministic mode of AR if available KBUILD_ARFLAGS := $(call ar-option,D) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 8b4d022ce0cbc..e59dc138b24ea 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -137,6 +137,9 @@ else KBUILD_CFLAGS += -mno-red-zone KBUILD_CFLAGS += -mcmodel=kernel + # Intel CET isn't enabled in the kernel + KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none) + # -funit-at-a-time shrinks the kernel .text considerably # unfortunately it makes reading oopses harder. KBUILD_CFLAGS += $(call cc-option,-funit-at-a-time) -- 2.47.2