[RFC PATCH v4 1/9] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking

[Yu-cheng Yu <yu-cheng.yu@intel.com>]

The user-mode indirect branch tracking support is done mostly by
GCC to insert ENDBR64/ENDBR32 instructions at branch targets.
The kernel provides CPUID enumeration, feature MSR setup and
the allocation of legacy bitmap.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
 arch/x86/Kconfig  | 12 ++++++++++++
 arch/x86/Makefile |  7 +++++++
 2 files changed, 19 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6377125543cc..2a0ff538a229 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1941,6 +1941,18 @@ config X86_INTEL_SHADOW_STACK_USER
 
 	  If unsure, say y.
 
+config X86_INTEL_BRANCH_TRACKING_USER
+	prompt "Intel Indirect Branch Tracking for user-mode"
+	def_bool n
+	depends on CPU_SUP_INTEL && X86_64
+	select X86_INTEL_CET
+	select ARCH_HAS_PROGRAM_PROPERTIES
+	---help---
+	  Indirect Branch Tracking provides hardware protection against return-/jmp-
+	  oriented programming attacks.
+
+	  If unsure, say y
+
 config EFI
 	bool "EFI runtime service support"
 	depends on ACPI
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index b28842b80295..ff652bba849f 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -159,6 +159,13 @@ ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
   endif
 endif
 
+# Check compiler ibt support
+ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
+  ifeq ($(call cc-option-yn, -fcf-protection=branch), n)
+      $(error CONFIG_X86_INTEL_BRANCH_TRACKING_USER not supported by compiler)
+  endif
+endif
+
 #
 # If the function graph tracer is used with mcount instead of fentry,
 # '-maccumulate-outgoing-args' is needed to prevent a GCC bug
-- 
2.17.1