arch/cc: Introduce a function to check for confidential computing features

In preparation for other confidential computing technologies, introduce
a generic helper function, cc_platform_has(), that can be used to
check for specific active confidential computing attributes, like
memory encryption. This is intended to eliminate having to add multiple
technology-specific checks to the code (e.g. if (sev_active() ||
tdx_active() || ... ).

 [ bp: s/_CC_PLATFORM_H/_LINUX_CC_PLATFORM_H/g ]

Co-developed-by: Andi Kleen <[email protected]>
Signed-off-by: Andi Kleen <[email protected]>
Co-developed-by: Kuppuswamy Sathyanarayanan <[email protected]>
Signed-off-by: Kuppuswamy Sathyanarayanan <[email protected]>
Signed-off-by: Tom Lendacky <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: tlendacky

arch/Kconfig

@@ -1234,6 +1234,9 @@ config RELR
 config ARCH_HAS_MEM_ENCRYPT
 	bool
 
+config ARCH_HAS_CC_PLATFORM
+	bool
+
 config HAVE_SPARSE_SYSCALL_NR
        bool
        help

include/linux/cc_platform.h

@@ -0,0 +1,88 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Confidential Computing Platform Capability checks
+ *
+ * Copyright (C) 2021 Advanced Micro Devices, Inc.
+ *
+ * Author: Tom Lendacky <[email protected]>
+ */
+
+#ifndef _LINUX_CC_PLATFORM_H
+#define _LINUX_CC_PLATFORM_H
+
+#include <linux/types.h>
+#include <linux/stddef.h>
+
+/**
+ * enum cc_attr - Confidential computing attributes
+ *
+ * These attributes represent confidential computing features that are
+ * currently active.
+ */
+enum cc_attr {
+	/**
+	 * @CC_ATTR_MEM_ENCRYPT: Memory encryption is active
+	 *
+	 * The platform/OS is running with active memory encryption. This
+	 * includes running either as a bare-metal system or a hypervisor
+	 * and actively using memory encryption or as a guest/virtual machine
+	 * and actively using memory encryption.
+	 *
+	 * Examples include SME, SEV and SEV-ES.
+	 */
+	CC_ATTR_MEM_ENCRYPT,
+
+	/**
+	 * @CC_ATTR_HOST_MEM_ENCRYPT: Host memory encryption is active
+	 *
+	 * The platform/OS is running as a bare-metal system or a hypervisor
+	 * and actively using memory encryption.
+	 *
+	 * Examples include SME.
+	 */
+	CC_ATTR_HOST_MEM_ENCRYPT,
+
+	/**
+	 * @CC_ATTR_GUEST_MEM_ENCRYPT: Guest memory encryption is active
+	 *
+	 * The platform/OS is running as a guest/virtual machine and actively
+	 * using memory encryption.
+	 *
+	 * Examples include SEV and SEV-ES.
+	 */
+	CC_ATTR_GUEST_MEM_ENCRYPT,
+
+	/**
+	 * @CC_ATTR_GUEST_STATE_ENCRYPT: Guest state encryption is active
+	 *
+	 * The platform/OS is running as a guest/virtual machine and actively
+	 * using memory encryption and register state encryption.
+	 *
+	 * Examples include SEV-ES.
+	 */
+	CC_ATTR_GUEST_STATE_ENCRYPT,
+};
+
+#ifdef CONFIG_ARCH_HAS_CC_PLATFORM
+
+/**
+ * cc_platform_has() - Checks if the specified cc_attr attribute is active
+ * @attr: Confidential computing attribute to check
+ *
+ * The cc_platform_has() function will return an indicator as to whether the
+ * specified Confidential Computing attribute is currently active.
+ *
+ * Context: Any context
+ * Return:
+ * * TRUE  - Specified Confidential Computing attribute is active
+ * * FALSE - Specified Confidential Computing attribute is not active
+ */
+bool cc_platform_has(enum cc_attr attr);
+
+#else	/* !CONFIG_ARCH_HAS_CC_PLATFORM */
+
+static inline bool cc_platform_has(enum cc_attr attr) { return false; }
+
+#endif	/* CONFIG_ARCH_HAS_CC_PLATFORM */
+
+#endif	/* _LINUX_CC_PLATFORM_H */