[PATCH 2/7] x86: Add CONFIG option X86_LASS

[Yian Chen]

LASS is an Intel x86-64 only feature. Add CONFIG
option X86_LASS and flag DISABLE_LASS to choose
opt-in/out the feature from kernel binary.

CONFIG_X86_LASS is enabled by default because it
is a security feature which should have little
to no overhead or side effects. If any issues are
found with specific use cases, the CONFIG option
makes it easy to disable.

Signed-off-by: Yian Chen <yian.chen@xxxxxxxxx>
Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
---
 arch/x86/Kconfig                               | 10 ++++++++++
 arch/x86/include/asm/disabled-features.h       |  8 +++++++-
 tools/arch/x86/include/asm/disabled-features.h |  8 +++++++-
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3604074a878b..38b1497afd75 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1826,6 +1826,16 @@ config ARCH_USES_PG_UNCACHED
 	def_bool y
 	depends on X86_PAT
 
+config X86_LASS
+	def_bool y
+	prompt "Linear Address Space Separation"
+	depends on X86_64 && CPU_SUP_INTEL
+	help
+	  Linear Address Space Separation (LASS) is a processor
+	  feature that mitigates address space layout probes.
+
+	  if unsure, say Y.
+
 config X86_UMIP
 	def_bool y
 	prompt "User Mode Instruction Prevention" if EXPERT
diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index c44b56f7ffba..0cad37d59e0f 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -16,6 +16,12 @@
 # define DISABLE_UMIP	(1<<(X86_FEATURE_UMIP & 31))
 #endif
 
+#ifdef CONFIG_X86_LASS
+# define DISABLE_LASS	0
+#else
+# define DISABLE_LASS	(1<<(X86_FEATURE_LASS & 31))
+#endif
+
 #ifdef CONFIG_X86_64
 # define DISABLE_VME		(1<<(X86_FEATURE_VME & 31))
 # define DISABLE_K6_MTRR	(1<<(X86_FEATURE_K6_MTRR & 31))
@@ -115,7 +121,7 @@
 #define DISABLED_MASK10	0
 #define DISABLED_MASK11	(DISABLE_RETPOLINE|DISABLE_RETHUNK|DISABLE_UNRET| \
 			 DISABLE_CALL_DEPTH_TRACKING)
-#define DISABLED_MASK12	0
+#define DISABLED_MASK12	(DISABLE_LASS)
 #define DISABLED_MASK13	0
 #define DISABLED_MASK14	0
 #define DISABLED_MASK15	0
diff --git a/tools/arch/x86/include/asm/disabled-features.h b/tools/arch/x86/include/asm/disabled-features.h
index c44b56f7ffba..0cad37d59e0f 100644
--- a/tools/arch/x86/include/asm/disabled-features.h
+++ b/tools/arch/x86/include/asm/disabled-features.h
@@ -16,6 +16,12 @@
 # define DISABLE_UMIP	(1<<(X86_FEATURE_UMIP & 31))
 #endif
 
+#ifdef CONFIG_X86_LASS
+# define DISABLE_LASS	0
+#else
+# define DISABLE_LASS	(1<<(X86_FEATURE_LASS & 31))
+#endif
+
 #ifdef CONFIG_X86_64
 # define DISABLE_VME		(1<<(X86_FEATURE_VME & 31))
 # define DISABLE_K6_MTRR	(1<<(X86_FEATURE_K6_MTRR & 31))
@@ -115,7 +121,7 @@
 #define DISABLED_MASK10	0
 #define DISABLED_MASK11	(DISABLE_RETPOLINE|DISABLE_RETHUNK|DISABLE_UNRET| \
 			 DISABLE_CALL_DEPTH_TRACKING)
-#define DISABLED_MASK12	0
+#define DISABLED_MASK12	(DISABLE_LASS)
 #define DISABLED_MASK13	0
 #define DISABLED_MASK14	0
 #define DISABLED_MASK15	0
-- 
2.34.1