x86/cpu: Enable Key Locker and add a chicken bit

Introduce a new config option to include the enabling codes at build-time.

Also, add a new command-line parameter -- 'nokeylocker' to disable the
feature at boot-time.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

Documentation/admin-guide/kernel-parameters.txt

@@ -3226,6 +3226,8 @@
 
 	nohugeiomap	[KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
 
+	nokeylocker	[X86] Disables Key Locker hardware feature.
+
 	nosmt		[KNL,S390] Disable symmetric multithreading (SMT).
 			Equivalent to smt=1.
 

arch/x86/Kconfig

@@ -1886,6 +1886,20 @@ config X86_INTEL_MEMORY_PROTECTION_KEYS
 
 	  If unsure, say y.
 
+config X86_KL
+	prompt "Key Locker" if EXPERT
+	def_bool y
+	depends on CPU_SUP_INTEL
+	help
+	  Key Locker is a new security feature to protect a data-encryption
+	  key for the Advanced Encryption Standard (AES) algorithm.
+
+	  When enabled, every CPU has a unique internal key to wrap the AES
+	  key into an encoded format.  The internal key is not accessible
+	  to software once loaded.
+
+	  If unsure, say y.
+
 choice
 	prompt "TSX enable mode"
 	depends on CPU_SUP_INTEL

arch/x86/include/asm/disabled-features.h

@@ -44,7 +44,11 @@
 # define DISABLE_OSPKE		(1<<(X86_FEATURE_OSPKE & 31))
 #endif /* CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS */
 
-#define DISABLE_KL		(1<<(X86_FEATURE_KL & 31))
+#ifdef CONFIG_X86_KL
+# define DISABLE_KL		0
+#else
+# define DISABLE_KL		(1<<(X86_FEATURE_KL & 31))
+#endif
 
 #ifdef CONFIG_X86_5LEVEL
 # define DISABLE_LA57	0

arch/x86/kernel/cpu/common.c

@@ -355,6 +355,23 @@ static __always_inline void setup_umip(struct cpuinfo_x86 *c)
 /* These bits should not change their value after CPU init is finished. */
 static const unsigned long cr4_pinned_mask =
 	X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP | X86_CR4_FSGSBASE;
+
+static __init int x86_nokeylocker_setup(char *arg)
+{
+	/* Expect an exact match without trailing characters */
+	if (strlen(arg))
+		return 0;
+
+	if (!cpu_feature_enabled(X86_FEATURE_KL) ||
+	    !boot_cpu_has(X86_FEATURE_KL))
+		return 1;
+
+	setup_clear_cpu_cap(X86_FEATURE_KL);
+	pr_info("x86/keylocker: Disabled by kernel command line\n");
+	return 1;
+}
+__setup("nokeylocker", x86_nokeylocker_setup);
+
 static DEFINE_STATIC_KEY_FALSE_RO(cr_pinning);
 static unsigned long cr4_pinned_bits __ro_after_init;