efi: Make rng_seed table handling local to efi.c

Move the rng_seed table address from struct efi into a static global
variable in efi.c, which is the only place we ever refer to it anyway.
This reduces the footprint of struct efi, which is a r/w data structure
that is shared with the world.

Tested-by: Tony Luck <tony.luck@intel.com> # arch/ia64
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/efi.c

@@ -44,13 +44,14 @@ struct efi __read_mostly efi = {
 	.config_table		= EFI_INVALID_TABLE_ADDR,
 	.esrt			= EFI_INVALID_TABLE_ADDR,
 	.mem_attr_table		= EFI_INVALID_TABLE_ADDR,
-	.rng_seed		= EFI_INVALID_TABLE_ADDR,
 	.tpm_log		= EFI_INVALID_TABLE_ADDR,
 	.tpm_final_log		= EFI_INVALID_TABLE_ADDR,
 	.mem_reserve		= EFI_INVALID_TABLE_ADDR,
 };
 EXPORT_SYMBOL(efi);
 
+static unsigned long __ro_after_init rng_seed = EFI_INVALID_TABLE_ADDR;
+
 struct mm_struct efi_mm = {
 	.mm_rb			= RB_ROOT,
 	.mm_users		= ATOMIC_INIT(2),
@@ -467,7 +468,7 @@ static __initdata efi_config_table_type_t common_tables[] = {
 	{SMBIOS3_TABLE_GUID, "SMBIOS 3.0", &efi.smbios3},
 	{EFI_SYSTEM_RESOURCE_TABLE_GUID, "ESRT", &efi.esrt},
 	{EFI_MEMORY_ATTRIBUTES_TABLE_GUID, "MEMATTR", &efi.mem_attr_table},
-	{LINUX_EFI_RANDOM_SEED_TABLE_GUID, "RNG", &efi.rng_seed},
+	{LINUX_EFI_RANDOM_SEED_TABLE_GUID, "RNG", &rng_seed},
 	{LINUX_EFI_TPM_EVENT_LOG_GUID, "TPMEventLog", &efi.tpm_log},
 	{LINUX_EFI_TPM_FINAL_LOG_GUID, "TPMFinalLog", &efi.tpm_final_log},
 	{LINUX_EFI_MEMRESERVE_TABLE_GUID, "MEMRESERVE", &efi.mem_reserve},
@@ -535,20 +536,19 @@ int __init efi_config_parse_tables(void *config_tables, int count, int sz,
 	pr_cont("\n");
 	set_bit(EFI_CONFIG_TABLES, &efi.flags);
 
-	if (efi.rng_seed != EFI_INVALID_TABLE_ADDR) {
+	if (rng_seed != EFI_INVALID_TABLE_ADDR) {
 		struct linux_efi_random_seed *seed;
 		u32 size = 0;
 
-		seed = early_memremap(efi.rng_seed, sizeof(*seed));
+		seed = early_memremap(rng_seed, sizeof(*seed));
 		if (seed != NULL) {
 			size = seed->size;
 			early_memunmap(seed, sizeof(*seed));
 		} else {
 			pr_err("Could not map UEFI random seed!\n");
 		}
 		if (size > 0) {
-			seed = early_memremap(efi.rng_seed,
-					      sizeof(*seed) + size);
+			seed = early_memremap(rng_seed, sizeof(*seed) + size);
 			if (seed != NULL) {
 				pr_notice("seeding entropy pool\n");
 				add_bootloader_randomness(seed->bits, seed->size);
@@ -1048,16 +1048,15 @@ static int update_efi_random_seed(struct notifier_block *nb,
 	if (!kexec_in_progress)
 		return NOTIFY_DONE;
 
-	seed = memremap(efi.rng_seed, sizeof(*seed), MEMREMAP_WB);
+	seed = memremap(rng_seed, sizeof(*seed), MEMREMAP_WB);
 	if (seed != NULL) {
 		size = min(seed->size, EFI_RANDOM_SEED_SIZE);
 		memunmap(seed);
 	} else {
 		pr_err("Could not map UEFI random seed!\n");
 	}
 	if (size > 0) {
-		seed = memremap(efi.rng_seed, sizeof(*seed) + size,
-				MEMREMAP_WB);
+		seed = memremap(rng_seed, sizeof(*seed) + size, MEMREMAP_WB);
 		if (seed != NULL) {
 			seed->size = size;
 			get_random_bytes(seed->bits, seed->size);
@@ -1073,9 +1072,9 @@ static struct notifier_block efi_random_seed_nb = {
 	.notifier_call = update_efi_random_seed,
 };
 
-static int register_update_efi_random_seed(void)
+static int __init register_update_efi_random_seed(void)
 {
-	if (efi.rng_seed == EFI_INVALID_TABLE_ADDR)
+	if (rng_seed == EFI_INVALID_TABLE_ADDR)
 		return 0;
 	return register_reboot_notifier(&efi_random_seed_nb);
 }

include/linux/efi.h

@@ -540,7 +540,6 @@ extern struct efi {
 	unsigned long config_table;	/* config tables */
 	unsigned long esrt;		/* ESRT table */
 	unsigned long mem_attr_table;	/* memory attributes table */
-	unsigned long rng_seed;		/* UEFI firmware random seed */
 	unsigned long tpm_log;		/* TPM2 Event Log table */
 	unsigned long tpm_final_log;	/* TPM2 Final Events Log table */
 	unsigned long mem_reserve;	/* Linux EFI memreserve table */