[RFC PATCH 5/8] x86/cpu: Add a config option and a chicken bit for Key Locker

[Chang S. Bae]

Add a kernel config option to enable the feature (disabled by default) at
compile-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@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 Documentation/admin-guide/kernel-parameters.txt |  2 ++
 arch/x86/Kconfig                                | 14 ++++++++++++++
 arch/x86/kernel/cpu/common.c                    | 16 ++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 44fde25bb221..c389ad8fb9de 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3220,6 +3220,8 @@
 
 	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.
 
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index fbf26e0f7a6a..7623af32f919 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1886,6 +1886,20 @@ config X86_INTEL_MEMORY_PROTECTION_KEYS
 
 	  If unsure, say y.
 
+config X86_KEYLOCKER
+	prompt "Key Locker"
+	def_bool n
+	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
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a446d5aff08f..ba5bd79fbac2 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -354,6 +354,22 @@ 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_KEYLOCKER))
+		return 1;
+
+	setup_clear_cpu_cap(X86_FEATURE_KEYLOCKER);
+	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;
 
-- 
2.17.1