[PATCH 3/8] x86/sev: Add an x86 version of cc_platform_has()

[Borislav Petkov]

From: Tom Lendacky <thomas.lendacky@xxxxxxx>

Introduce an x86 version of the cc_platform_has() function. This will be
used to replace vendor specific calls like sme_active(), sev_active(),
etc.

Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 arch/x86/Kconfig                   |  1 +
 arch/x86/include/asm/mem_encrypt.h |  1 +
 arch/x86/kernel/Makefile           |  6 +++
 arch/x86/kernel/cc_platform.c      | 69 ++++++++++++++++++++++++++++++
 arch/x86/mm/mem_encrypt.c          |  1 +
 5 files changed, 78 insertions(+)
 create mode 100644 arch/x86/kernel/cc_platform.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ab83c22d274e..9f190ec4f953 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1518,6 +1518,7 @@ config AMD_MEM_ENCRYPT
 	select ARCH_HAS_FORCE_DMA_UNENCRYPTED
 	select INSTRUCTION_DECODER
 	select ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
+	select ARCH_HAS_CC_PLATFORM
 	help
 	  Say yes to enable support for the encryption of system memory.
 	  This requires an AMD processor that supports Secure Memory
diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 9c80c68d75b5..3fb9f5ebefa4 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -13,6 +13,7 @@
 #ifndef __ASSEMBLY__
 
 #include <linux/init.h>
+#include <linux/cc_platform.h>
 
 #include <asm/bootparam.h>
 
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 8f4e8fa6ed75..2ff3e600f426 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -21,6 +21,7 @@ CFLAGS_REMOVE_ftrace.o = -pg
 CFLAGS_REMOVE_early_printk.o = -pg
 CFLAGS_REMOVE_head64.o = -pg
 CFLAGS_REMOVE_sev.o = -pg
+CFLAGS_REMOVE_cc_platform.o = -pg
 endif
 
 KASAN_SANITIZE_head$(BITS).o				:= n
@@ -29,6 +30,7 @@ KASAN_SANITIZE_dumpstack_$(BITS).o			:= n
 KASAN_SANITIZE_stacktrace.o				:= n
 KASAN_SANITIZE_paravirt.o				:= n
 KASAN_SANITIZE_sev.o					:= n
+KASAN_SANITIZE_cc_platform.o				:= n
 
 # With some compiler versions the generated code results in boot hangs, caused
 # by several compilation units. To be safe, disable all instrumentation.
@@ -47,6 +49,7 @@ endif
 KCOV_INSTRUMENT		:= n
 
 CFLAGS_head$(BITS).o	+= -fno-stack-protector
+CFLAGS_cc_platform.o	+= -fno-stack-protector
 
 CFLAGS_irq.o := -I $(srctree)/$(src)/../include/asm/trace
 
@@ -147,6 +150,9 @@ obj-$(CONFIG_UNWINDER_FRAME_POINTER)	+= unwind_frame.o
 obj-$(CONFIG_UNWINDER_GUESS)		+= unwind_guess.o
 
 obj-$(CONFIG_AMD_MEM_ENCRYPT)		+= sev.o
+
+obj-$(CONFIG_ARCH_HAS_CC_PLATFORM)	+= cc_platform.o
+
 ###
 # 64 bit specific files
 ifeq ($(CONFIG_X86_64),y)
diff --git a/arch/x86/kernel/cc_platform.c b/arch/x86/kernel/cc_platform.c
new file mode 100644
index 000000000000..03bb2f343ddb
--- /dev/null
+++ b/arch/x86/kernel/cc_platform.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Confidential Computing Platform Capability checks
+ *
+ * Copyright (C) 2021 Advanced Micro Devices, Inc.
+ *
+ * Author: Tom Lendacky <thomas.lendacky@xxxxxxx>
+ */
+
+#include <linux/export.h>
+#include <linux/cc_platform.h>
+#include <linux/mem_encrypt.h>
+
+#include <asm/processor.h>
+
+static bool __maybe_unused intel_cc_platform_has(enum cc_attr attr)
+{
+#ifdef CONFIG_INTEL_TDX_GUEST
+	return false;
+#else
+	return false;
+#endif
+}
+
+/*
+ * SME and SEV are very similar but they are not the same, so there are
+ * times that the kernel will need to distinguish between SME and SEV. The
+ * cc_platform_has() function is used for this.  When a distinction isn't
+ * needed, the CC_ATTR_MEM_ENCRYPT attribute can be used.
+ *
+ * The trampoline code is a good example for this requirement.  Before
+ * paging is activated, SME will access all memory as decrypted, but SEV
+ * will access all memory as encrypted.  So, when APs are being brought
+ * up under SME the trampoline area cannot be encrypted, whereas under SEV
+ * the trampoline area must be encrypted.
+ */
+static bool amd_cc_platform_has(enum cc_attr attr)
+{
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+	switch (attr) {
+	case CC_ATTR_MEM_ENCRYPT:
+		return sme_me_mask;
+
+	case CC_ATTR_HOST_MEM_ENCRYPT:
+		return sme_me_mask && !(sev_status & MSR_AMD64_SEV_ENABLED);
+
+	case CC_ATTR_GUEST_MEM_ENCRYPT:
+		return sev_status & MSR_AMD64_SEV_ENABLED;
+
+	case CC_ATTR_GUEST_STATE_ENCRYPT:
+		return sev_status & MSR_AMD64_SEV_ES_ENABLED;
+
+	default:
+		return false;
+	}
+#else
+	return false;
+#endif
+}
+
+
+bool cc_platform_has(enum cc_attr attr)
+{
+	if (sme_me_mask)
+		return amd_cc_platform_has(attr);
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(cc_platform_has);
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index ff08dc463634..e29b1418d00c 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -20,6 +20,7 @@
 #include <linux/bitops.h>
 #include <linux/dma-mapping.h>
 #include <linux/virtio_config.h>
+#include <linux/cc_platform.h>
 
 #include <asm/tlbflush.h>
 #include <asm/fixmap.h>
-- 
2.29.2