[RFC PATCH 06/16] x86/efi: Generating random HMAC key for siging hibernate image

["Lee, Chun-Yi" <joeyli.kernel@gmail.com>]

This patch adds codes in EFI stub for generating and storing the
HMAC key in EFI boot service variable for signing hibernate image.

Per rcf2104, the length of HMAC-SHA1 hash result is 20 bytes, and
it recommended the length of key the same with hash rsult, means
also 20 bytes. Using longer key would not significantly increase
the function strength. Due to the nvram space is limited in some
UEFI machines, so using the minimal recommended length 20 bytes
key that will stored in boot service variable.

For generating a messy number as a 20 bytes key, the codes in EFI
stub gets u32 random number five time and every random number is
rolling that last u32 random number as entropy.

The HMAC key stored in EFI boot service variable, the GUID is
S4SignKey-fe141863-c070-478e-b8a3-878a5dc9ef21.

Signed-off-by: Lee, Chun-Yi <jlee@suse.com>
---
 arch/x86/boot/compressed/eboot.c | 57 ++++++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/suspend.h   |  9 +++++++
 include/linux/suspend.h          |  3 +++
 3 files changed, 69 insertions(+)

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index 0ffb6db..97b356f 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -12,6 +12,7 @@
 #include <asm/efi.h>
 #include <asm/setup.h>
 #include <asm/desc.h>
+#include <asm/suspend.h>
 
 #include "../string.h"
 #include "eboot.h"
@@ -1383,6 +1384,60 @@ free_mem_map:
 	return status;
 }
 
+#ifdef CONFIG_HIBERNATE_VERIFICATION
+#define SWSUSP_KEY \
+	((efi_char16_t [10]) { 'S', 'W', 'S', 'U', 'S', 'P', 'K', 'e', 'y', 0 })
+#define SWSUSP_KEY_ATTRIBUTE	(EFI_VARIABLE_NON_VOLATILE | \
+				EFI_VARIABLE_BOOTSERVICE_ACCESS)
+
+static void setup_swsusp_keys(struct boot_params *params)
+{
+	unsigned long key_size, attributes;
+	struct swsusp_keys *swsusp_keys;
+	efi_status_t status;
+
+	/* Allocate setup_data to carry keys */
+	status = efi_call_early(allocate_pool, EFI_LOADER_DATA,
+				sizeof(struct swsusp_keys), &swsusp_keys);
+	if (status != EFI_SUCCESS) {
+		efi_printk(sys_table, "Failed to alloc mem for swsusp_keys\n");
+		return;
+	}
+
+	memset(swsusp_keys, 0, sizeof(struct swsusp_keys));
+
+	status = efi_call_early(get_variable, SWSUSP_KEY, &EFI_SWSUSP_GUID,
+				&attributes, &key_size, swsusp_keys->swsusp_key);
+	if (status == EFI_SUCCESS && attributes != SWSUSP_KEY_ATTRIBUTE) {
+		efi_printk(sys_table, "A swsusp key is not boot service variable\n");
+		memset(swsusp_keys->swsusp_key, 0, SWSUSP_DIGEST_SIZE);
+		status = efi_call_early(set_variable, SWSUSP_KEY,
+					&EFI_SWSUSP_GUID, attributes, 0, NULL);
+		if (status == EFI_SUCCESS) {
+			efi_printk(sys_table, "Cleaned existing swsusp key\n");
+			status = EFI_NOT_FOUND;
+		}
+	}
+
+	if (status != EFI_SUCCESS) {
+		efi_printk(sys_table, "Failed to get existing swsusp key\n");
+
+		efi_get_random_key(sys_table, params, swsusp_keys->swsusp_key,
+				   SWSUSP_DIGEST_SIZE);
+
+		status = efi_call_early(set_variable, SWSUSP_KEY,
+					&EFI_SWSUSP_GUID,
+					SWSUSP_KEY_ATTRIBUTE,
+					SWSUSP_DIGEST_SIZE,
+					swsusp_keys->swsusp_key);
+		if (status != EFI_SUCCESS)
+			efi_printk(sys_table, "Failed to set swsusp key\n");
+	}
+}
+#else
+static void setup_swsusp_keys(struct boot_params *params) {}
+#endif
+
 /*
  * On success we return a pointer to a boot_params structure, and NULL
  * on failure.
@@ -1420,6 +1475,8 @@ struct boot_params *efi_main(struct efi_config *c,
 
 	setup_efi_pci(boot_params);
 
+	setup_swsusp_keys(boot_params);
+
 	status = efi_call_early(allocate_pool, EFI_LOADER_DATA,
 				sizeof(*gdt), (void **)&gdt);
 	if (status != EFI_SUCCESS) {
diff --git a/arch/x86/include/asm/suspend.h b/arch/x86/include/asm/suspend.h
index 2fab6c2..b0c3f68 100644
--- a/arch/x86/include/asm/suspend.h
+++ b/arch/x86/include/asm/suspend.h
@@ -3,3 +3,12 @@
 #else
 # include <asm/suspend_64.h>
 #endif
+
+#ifdef CONFIG_HIBERNATE_VERIFICATION
+#include <linux/suspend.h>
+
+struct swsusp_keys {
+	unsigned long skey_status;
+	u8 swsusp_key[SWSUSP_DIGEST_SIZE];
+};
+#endif
diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index 6cd2a48..1ec7d11 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -328,6 +328,9 @@ struct platform_hibernation_ops {
 
 #ifdef CONFIG_HIBERNATION
 
+#define EFI_SWSUSP_GUID \
+	EFI_GUID(0xfe141863, 0xc070, 0x478e, 0xb8, 0xa3, 0x87, 0x8a, 0x5d, 0xc9, 0xef, 0x21)
+
 /* HMAC Algorithm of Hibernate Signature */
 #define SWSUSP_HMAC		"hmac(sha1)"
 #define SWSUSP_DIGEST_SIZE	20
-- 
1.8.4.5