[RFC PATCH 2/3] efi: Reserve confidential computing secret area

[Dov Murik <dovmurik@xxxxxxxxxxxxx>]

When efi-stub copies an EFI-provided confidential computing secret area,
reserve that memory block for future use within the kernel.

Cc: Laszlo Ersek <lersek@xxxxxxxxxx>
Cc: Ashish Kalra <ashish.kalra@xxxxxxx>
Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: James Bottomley <jejb@xxxxxxxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: linux-efi@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Dov Murik <dovmurik@xxxxxxxxxxxxx>
---
 drivers/firmware/efi/Makefile                 |  2 +-
 drivers/firmware/efi/confidential-computing.c | 41 +++++++++++++++++++
 drivers/firmware/efi/efi.c                    |  5 +++
 include/linux/efi.h                           |  4 ++
 4 files changed, 51 insertions(+), 1 deletion(-)
 create mode 100644 drivers/firmware/efi/confidential-computing.c

diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
index 467e94259679..63f21f7351da 100644
--- a/drivers/firmware/efi/Makefile
+++ b/drivers/firmware/efi/Makefile
@@ -12,7 +12,7 @@ KASAN_SANITIZE_runtime-wrappers.o	:= n
 
 obj-$(CONFIG_ACPI_BGRT) 		+= efi-bgrt.o
 obj-$(CONFIG_EFI)			+= efi.o vars.o reboot.o memattr.o tpm.o
-obj-$(CONFIG_EFI)			+= memmap.o
+obj-$(CONFIG_EFI)			+= memmap.o confidential-computing.o
 ifneq ($(CONFIG_EFI_CAPSULE_LOADER),)
 obj-$(CONFIG_EFI)			+= capsule.o
 endif
diff --git a/drivers/firmware/efi/confidential-computing.c b/drivers/firmware/efi/confidential-computing.c
new file mode 100644
index 000000000000..e6bb4d1e8f17
--- /dev/null
+++ b/drivers/firmware/efi/confidential-computing.c
@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Confidential computing secret area handling
+ *
+ * Copyright (C) 2021 IBM Corporation
+ * Author: Dov Murik <dovmurik@xxxxxxxxxxxxx>
+ */
+
+#define pr_fmt(fmt) "efi: " fmt
+
+#include <linux/efi.h>
+#include <linux/init.h>
+#include <linux/memblock.h>
+#include <asm/early_ioremap.h>
+
+/*
+ * Reserve the confidential computing secret area memory
+ */
+int __init efi_confidential_computing_secret_area_reserve(void)
+{
+	struct linux_efi_confidential_computing_secret_area *secret_area;
+	unsigned long secret_area_size;
+
+	if (efi.confidential_computing_secret == EFI_INVALID_TABLE_ADDR)
+		return 0;
+
+	secret_area = early_memremap(efi.confidential_computing_secret, sizeof(*secret_area));
+	if (!secret_area) {
+		pr_err("Failed to map confidential computing secret area\n");
+		efi.confidential_computing_secret = EFI_INVALID_TABLE_ADDR;
+		return -ENOMEM;
+	}
+
+	secret_area_size = sizeof(*secret_area) + secret_area->size;
+	memblock_reserve(efi.confidential_computing_secret, secret_area_size);
+
+	pr_info("Reserved memory of EFI-provided confidential computing secret area");
+
+	early_memunmap(secret_area, sizeof(*secret_area));
+	return 0;
+}
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 4b7ee3fa9224..da36333e5c9f 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -526,6 +526,9 @@ static const efi_config_table_type_t common_tables[] __initconst = {
 #ifdef CONFIG_LOAD_UEFI_KEYS
 	{LINUX_EFI_MOK_VARIABLE_TABLE_GUID,	&efi.mokvar_table,	"MOKvar"	},
 #endif
+	{LINUX_EFI_CONFIDENTIAL_COMPUTING_SECRET_AREA_GUID,
+						&efi.confidential_computing_secret,
+									"ConfCompSecret"},
 	{},
 };
 
@@ -613,6 +616,8 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables,
 
 	efi_tpm_eventlog_init();
 
+	efi_confidential_computing_secret_area_reserve();
+
 	if (mem_reserve != EFI_INVALID_TABLE_ADDR) {
 		unsigned long prsv = mem_reserve;
 
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 4f647f1ee298..e9740bd16db0 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -551,6 +551,8 @@ extern struct efi {
 	unsigned long			tpm_log;		/* TPM2 Event Log table */
 	unsigned long			tpm_final_log;		/* TPM2 Final Events Log table */
 	unsigned long			mokvar_table;		/* MOK variable config table */
+	unsigned long			confidential_computing_secret;	/* Confidential computing */
+									/* secret table           */
 
 	efi_get_time_t			*get_time;
 	efi_set_time_t			*set_time;
@@ -1190,6 +1192,8 @@ extern int efi_tpm_final_log_size;
 
 extern unsigned long rci2_table_phys;
 
+extern int efi_confidential_computing_secret_area_reserve(void);
+
 /*
  * efi_runtime_service() function identifiers.
  * "NONE" is used by efi_recover_from_page_fault() to check if the page
-- 
2.25.1