efi: avoid efivars layer when loading SSDTs from variables

The efivars intermediate variable access layer provides an abstraction
that permits the EFI variable store to be replaced by something else
that implements a compatible interface, and caches all variables in the
variable store for fast access via the efivarfs pseudo-filesystem.

The SSDT override feature does not take advantage of either feature, as
it is only used when the generic EFI implementation of efivars is used,
and it traverses all variables only once to find the ones it is
interested in, and frees all data structures that the efivars layer
keeps right after.

So in this case, let's just call EFI's code directly, using the function
pointers in struct efi.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/efi.c

@@ -202,7 +202,7 @@ static void generic_ops_unregister(void)
 }
 
 #ifdef CONFIG_EFI_CUSTOM_SSDT_OVERLAYS
-#define EFIVAR_SSDT_NAME_MAX	16
+#define EFIVAR_SSDT_NAME_MAX	16UL
 static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX] __initdata;
 static int __init efivar_ssdt_setup(char *str)
 {
@@ -219,83 +219,62 @@ static int __init efivar_ssdt_setup(char *str)
 }
 __setup("efivar_ssdt=", efivar_ssdt_setup);
 
-static __init int efivar_ssdt_iter(efi_char16_t *name, efi_guid_t vendor,
-				   unsigned long name_size, void *data)
-{
-	struct efivar_entry *entry;
-	struct list_head *list = data;
-	char utf8_name[EFIVAR_SSDT_NAME_MAX];
-	int limit = min_t(unsigned long, EFIVAR_SSDT_NAME_MAX, name_size);
-
-	ucs2_as_utf8(utf8_name, name, limit - 1);
-	if (strncmp(utf8_name, efivar_ssdt, limit) != 0)
-		return 0;
-
-	entry = kmalloc(sizeof(*entry), GFP_KERNEL);
-	if (!entry)
-		return 0;
-
-	memcpy(entry->var.VariableName, name, name_size);
-	memcpy(&entry->var.VendorGuid, &vendor, sizeof(efi_guid_t));
-
-	efivar_entry_add(entry, list);
-
-	return 0;
-}
-
 static __init int efivar_ssdt_load(void)
 {
-	LIST_HEAD(entries);
-	struct efivar_entry *entry, *aux;
-	unsigned long size;
-	void *data;
-	int ret;
+	unsigned long name_size = 256;
+	efi_char16_t *name = NULL;
+	efi_status_t status;
+	efi_guid_t guid;
 
 	if (!efivar_ssdt[0])
 		return 0;
 
-	ret = efivar_init(efivar_ssdt_iter, &entries, true, &entries);
-
-	list_for_each_entry_safe(entry, aux, &entries, list) {
-		pr_info("loading SSDT from variable %s-%pUl\n", efivar_ssdt,
-			&entry->var.VendorGuid);
+	name = kzalloc(name_size, GFP_KERNEL);
+	if (!name)
+		return -ENOMEM;
 
-		list_del(&entry->list);
+	for (;;) {
+		char utf8_name[EFIVAR_SSDT_NAME_MAX];
+		unsigned long data_size = 0;
+		void *data;
+		int limit;
 
-		ret = efivar_entry_size(entry, &size);
-		if (ret) {
-			pr_err("failed to get var size\n");
-			goto free_entry;
+		status = efi.get_next_variable(&name_size, name, &guid);
+		if (status == EFI_NOT_FOUND) {
+			break;
+		} else if (status == EFI_BUFFER_TOO_SMALL) {
+			name = krealloc(name, name_size, GFP_KERNEL);
+			if (!name)
+				return -ENOMEM;
+			continue;
 		}
 
-		data = kmalloc(size, GFP_KERNEL);
-		if (!data) {
-			ret = -ENOMEM;
-			goto free_entry;
-		}
+		limit = min(EFIVAR_SSDT_NAME_MAX, name_size);
+		ucs2_as_utf8(utf8_name, name, limit - 1);
+		if (strncmp(utf8_name, efivar_ssdt, limit) != 0)
+			continue;
 
-		ret = efivar_entry_get(entry, NULL, &size, data);
-		if (ret) {
-			pr_err("failed to get var data\n");
-			goto free_data;
-		}
+		pr_info("loading SSDT from variable %s-%pUl\n", efivar_ssdt, &guid);
 
-		ret = acpi_load_table(data, NULL);
-		if (ret) {
-			pr_err("failed to load table: %d\n", ret);
-			goto free_data;
-		}
+		status = efi.get_variable(name, &guid, NULL, &data_size, NULL);
+		if (status != EFI_BUFFER_TOO_SMALL || !data_size)
+			return -EIO;
 
-		goto free_entry;
+		data = kmalloc(data_size, GFP_KERNEL);
+		if (!data)
+			return -ENOMEM;
 
-free_data:
+		status = efi.get_variable(name, &guid, NULL, &data_size, data);
+		if (status == EFI_SUCCESS) {
+			acpi_status ret = acpi_load_table(data, NULL);
+			if (ret)
+				pr_err("failed to load table: %u\n", ret);
+		} else {
+			pr_err("failed to get var data: 0x%lx\n", status);
+		}
 		kfree(data);
-
-free_entry:
-		kfree(entry);
 	}
-
-	return ret;
+	return 0;
 }
 #else
 static inline int efivar_ssdt_load(void) { return 0; }