[RFC PATCH 02/11] kbuild: Support FineIBT build

[joao@overdrivepizza.com]

From: Joao Moreira <joao@overdrivepizza.com>

Add FineIBT compilation flags to Makefiles, preserving translation
units which should not get it.

Signed-off-by: Joao Moreira <joao@overdrivepizza.com>
---
 arch/x86/Kconfig             | 10 ++++++++++
 arch/x86/Makefile            |  3 +++
 arch/x86/entry/vdso/Makefile |  5 +++++
 arch/x86/kernel/Makefile     |  1 +
 arch/x86/purgatory/Makefile  |  4 ++++
 5 files changed, 23 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b0142e01002e..37e49e9187a0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1872,6 +1872,16 @@ config X86_KERNEL_IBT
 	  does significantly reduce the number of ENDBR instructions in the
 	  kernel image.
 
+config CC_HAS_FINEIBT
+	def_bool $(cc-option, -fcf-protection=branch -mfine-ibt) && $(as-instr,endbr64)
+
+config X86_KERNEL_FINEIBT
+	prompt "Fine-grain Indirect Branch Tracking"
+	bool
+	depends on X86_KERNEL_IBT && CC_HAS_FINEIBT
+	help
+	  Build the kernel with Fine-grained IBT.
+
 config X86_INTEL_MEMORY_PROTECTION_KEYS
 	prompt "Memory Protection Keys"
 	def_bool y
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 63d50f65b828..768e318eb78f 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -73,6 +73,9 @@ ifeq ($(CONFIG_X86_KERNEL_IBT),y)
 #   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104816
 #
 KBUILD_CFLAGS += $(call cc-option,-fcf-protection=branch -fno-jump-tables)
+ifeq ($(CONFIG_X86_KERNEL_FINEIBT),y)
+KBUILD_CFLAGS += $(call cc-option, -mfine-ibt)
+endif
 else
 KBUILD_CFLAGS += $(call cc-option,-fcf-protection=none)
 endif
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 693f8b9031fb..3dce5571460e 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -91,7 +91,11 @@ ifneq ($(RETPOLINE_VDSO_CFLAGS),)
 endif
 endif
 
+ifdef CONFIG_X86_KERNEL_FINEIBT
+$(vobjs): KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS) -mfine-ibt,$(KBUILD_CFLAGS)) $(CFL)
+else
 $(vobjs): KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
+endif
 
 #
 # vDSO code runs in userspace and -pg doesn't help with profiling anyway.
@@ -151,6 +155,7 @@ KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 := $(filter-out $(CC_FLAGS_LTO),$(KBUILD_CFLAGS_32))
+KBUILD_CFLAGS_32 := $(filter-out -mfine-ibt,$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
 KBUILD_CFLAGS_32 += -fno-stack-protector
 KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index c41ef42adbe8..cb947569e9d8 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -148,6 +148,7 @@ obj-$(CONFIG_UNWINDER_FRAME_POINTER)	+= unwind_frame.o
 obj-$(CONFIG_UNWINDER_GUESS)		+= unwind_guess.o
 
 obj-$(CONFIG_AMD_MEM_ENCRYPT)		+= sev.o
+obj-$(CONFIG_X86_KERNEL_FINEIBT)	+= fineibt.o
 
 ###
 # 64 bit specific files
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index ae53d54d7959..e16b25a598ba 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -55,6 +55,10 @@ ifdef CONFIG_RETPOLINE
 PURGATORY_CFLAGS_REMOVE		+= $(RETPOLINE_CFLAGS)
 endif
 
+ifdef CONFIG_X86_KERNEL_FINEIBT
+PURGATORY_CFLAGS_REMOVE += -mfine-ibt
+endif
+
 CFLAGS_REMOVE_purgatory.o	+= $(PURGATORY_CFLAGS_REMOVE)
 CFLAGS_purgatory.o		+= $(PURGATORY_CFLAGS)
 
-- 
2.35.1