[PATCH v26 1/9] x86/cet/ibt: Add Kconfig option for Indirect Branch Tracking

[Yu-cheng Yu]

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>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
---
v25:
- Make CONFIG_X86_IBT depend on CONFIG_X86_SHADOW_STACK.

 arch/x86/Kconfig                         | 19 +++++++++++++++++++
 arch/x86/include/asm/disabled-features.h |  8 +++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 77d2e44995d7..6bb69fba0dad 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1965,6 +1965,25 @@ config X86_SHADOW_STACK
 
 	  If unsure, say N.
 
+config X86_IBT
+	prompt "Intel Indirect Branch Tracking"
+	def_bool n
+	depends on X86_SHADOW_STACK
+	depends on $(cc-option,-fcf-protection)
+	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 present on Tiger Lake family of
+	  processors released in 2020 or later.  Enabling this feature
+	  increases kernel text size by 3.7 KB.
+	  See Documentation/x86/intel_cet.rst for more information.
+
+	  If unsure, say N.
+
 config EFI
 	bool "EFI runtime service support"
 	depends on ACPI
diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index e5c6ed9373e8..07cc40d49947 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -74,6 +74,12 @@
 #define DISABLE_SHSTK	(1 << (X86_FEATURE_SHSTK & 31))
 #endif
 
+#ifdef CONFIG_X86_IBT
+#define DISABLE_IBT	0
+#else
+#define DISABLE_IBT	(1 << (X86_FEATURE_IBT & 31))
+#endif
+
 /*
  * Make sure to add features to the correct mask
  */
@@ -96,7 +102,7 @@
 #define DISABLED_MASK16	(DISABLE_PKU|DISABLE_OSPKE|DISABLE_LA57|DISABLE_UMIP| \
 			 DISABLE_ENQCMD|DISABLE_SHSTK)
 #define DISABLED_MASK17	0
-#define DISABLED_MASK18	0
+#define DISABLED_MASK18	(DISABLE_IBT)
 #define DISABLED_MASK19	0
 #define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 20)
 
-- 
2.21.0