The following commit has been merged into the x86/urgent branch of tip: Commit-ID: 20bf2b378729c4a0366a53e2018a0b70ace94bcd Gitweb: https://git.kernel.org/tip/20bf2b378729c4a0366a53e2018a0b70ace94bcd Author: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> AuthorDate: Thu, 28 Jan 2021 15:52:19 -06:00 Committer: Borislav Petkov <bp@xxxxxxx> CommitterDate: Fri, 29 Jan 2021 18:41:06 +01:00 x86/build: Disable CET instrumentation in the kernel 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 <nborisov@xxxxxxxx> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx> Tested-by: Nikolay Borisov <nborisov@xxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Cc: Seth Forshee <seth.forshee@xxxxxxxxxxxxx> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20210128215219.6kct3h2eiustncws@treble --- Makefile | 6 ------ arch/x86/Makefile | 3 +++ 2 files changed, 3 insertions(+), 6 deletions(-) diff --git a/Makefile b/Makefile index e0af7a4..51c2bf3 100644 --- a/Makefile +++ b/Makefile @@ -948,12 +948,6 @@ KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init) # change __FILE__ to the relative path from the srctree KBUILD_CPPFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) -# ensure -fcf-protection is disabled when using retpoline as it is -# incompatible with -mindirect-branch=thunk-extern -ifdef CONFIG_RETPOLINE -KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none) -endif - # include additional Makefiles when needed include-y := scripts/Makefile.extrawarn include-$(CONFIG_KASAN) += scripts/Makefile.kasan diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 7116da3..5857917 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -120,6 +120,9 @@ 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) endif ifdef CONFIG_X86_X32
