[PATCH v15 1/7] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking

[Yu-cheng Yu]

Introduce Kconfig option X86_BRANCH_TRACKING_USER.

Indirect Branch Tracking (IBT) provides protection against CALL-/JMP-
oriented programming attacks.  It is active when the kernel has this
feature enabled, and the processor and the application support it.
When this feature is enabled, legacy non-IBT applications continue to
work, but without IBT protection.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
 arch/x86/Kconfig | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 18fd8cb549ad..e27f0c19a4b3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1969,6 +1969,25 @@ config X86_SHADOW_STACK_USER
 
 	  If unsure, say N.
 
+config X86_BRANCH_TRACKING_USER
+	prompt "Intel Indirect Branch Tracking for user-mode"
+	def_bool n
+	depends on CPU_SUP_INTEL && X86_64
+	depends on $(cc-option,-fcf-protection)
+	select X86_CET
+	help
+	  Indirect Branch Tracking (IBT) provides protection against
+	  CALL-/JMP-oriented programming attacks.  It is active when
+	  the kernel has this feature enabled, and the processor and
+	  the application support it.  When this feature is enabled,
+	  legacy non-IBT applications continue to work, but without
+	  IBT protection.
+	  Support for this feature is only known to be present on
+	  processors released in 2020 or later.  CET features are also
+	  known to increase kernel text size by 3.7 KB.
+
+	  If unsure, say N.
+
 config EFI
 	bool "EFI runtime service support"
 	depends on ACPI
-- 
2.21.0