From 7f31a66e0ffb32ff16acaff70d27e1bd858dcaba 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 088dc5383dcf2..aa1424bebc308 100644 --- a/Makefile +++ b/Makefile @@ -844,12 +844,6 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init) # change __FILE__ to the relative path from the srctree KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) -# 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 3dc54d2f79c4e..4c8e9f12b0c4d 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -138,6 +138,9 @@ 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) -- 2.50.1