From: Josh Poimboeuf <[email protected]>
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 <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Reviewed-by: Nikolay Borisov <[email protected]>
Tested-by: Nikolay Borisov <[email protected]>
Cc: <[email protected]>
Cc: Seth Forshee <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Link: https://lkml.kernel.org/r/20210128215219.6kct3h2eiustncws@treble
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
Makefile | 6 ------
arch/x86/Makefile | 3 +++
2 files changed, 3 insertions(+), 6 deletions(-)
--- a/Makefile
+++ b/Makefile
@@ -830,12 +830,6 @@ KBUILD_CFLAGS += $(call cc-option,-Wer
# 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)
--- 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)
