efi: efivars: Fix variable writes without query_variable_store()

Commit bbc6d2c ("efi: vars: Switch to new wrapper layer")
refactored the efivars layer so that the 'business logic' related to
which UEFI variables affect the boot flow in which way could be moved
out of it, and into the efivarfs driver.

This inadvertently broke setting variables on firmware implementations
that lack the QueryVariableInfo() boot service, because we no longer
tolerate a EFI_UNSUPPORTED result from check_var_size() when calling
efivar_entry_set_get_size(), which now ends up calling check_var_size()
a second time inadvertently.

If QueryVariableInfo() is missing, we support writes of up to 64k -
let's move that logic into check_var_size(), and drop the redundant
call.

Cc: <stable@vger.kernel.org> # v6.0
Fixes: bbc6d2c ("efi: vars: Switch to new wrapper layer")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/vars.c

@@ -7,6 +7,7 @@
  */
 
 #include <linux/types.h>
+#include <linux/sizes.h>
 #include <linux/errno.h>
 #include <linux/init.h>
 #include <linux/module.h>
@@ -20,31 +21,30 @@ static struct efivars *__efivars;
 
 static DEFINE_SEMAPHORE(efivars_lock);
 
-efi_status_t check_var_size(u32 attributes, unsigned long size)
+static efi_status_t check_var_size(u32 attributes, unsigned long size)
 {
 	const struct efivar_operations *fops;
 
 	fops = __efivars->ops;
 
 	if (!fops->query_variable_store)
-		return EFI_UNSUPPORTED;
+		return (size <= SZ_64K) ? EFI_SUCCESS : EFI_OUT_OF_RESOURCES;
 
 	return fops->query_variable_store(attributes, size, false);
 }
-EXPORT_SYMBOL_NS_GPL(check_var_size, EFIVAR);
 
+static
 efi_status_t check_var_size_nonblocking(u32 attributes, unsigned long size)
 {
 	const struct efivar_operations *fops;
 
 	fops = __efivars->ops;
 
 	if (!fops->query_variable_store)
-		return EFI_UNSUPPORTED;
+		return (size <= SZ_64K) ? EFI_SUCCESS : EFI_OUT_OF_RESOURCES;
 
 	return fops->query_variable_store(attributes, size, true);
 }
-EXPORT_SYMBOL_NS_GPL(check_var_size_nonblocking, EFIVAR);
 
 /**
  * efivars_kobject - get the kobject for the registered efivars

fs/efivarfs/vars.c

@@ -651,22 +651,6 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
 	if (err)
 		return err;
 
-	/*
-	 * Ensure that the available space hasn't shrunk below the safe level
-	 */
-	status = check_var_size(attributes, *size + ucs2_strsize(name, 1024));
-	if (status != EFI_SUCCESS) {
-		if (status != EFI_UNSUPPORTED) {
-			err = efi_status_to_err(status);
-			goto out;
-		}
-
-		if (*size > 65536) {
-			err = -ENOSPC;
-			goto out;
-		}
-	}
-
 	status = efivar_set_variable_locked(name, vendor, attributes, *size,
 					    data, false);
 	if (status != EFI_SUCCESS) {

include/linux/efi.h

@@ -1085,9 +1085,6 @@ efi_status_t efivar_set_variable_locked(efi_char16_t *name, efi_guid_t *vendor,
 efi_status_t efivar_set_variable(efi_char16_t *name, efi_guid_t *vendor,
 				 u32 attr, unsigned long data_size, void *data);
 
-efi_status_t check_var_size(u32 attributes, unsigned long size);
-efi_status_t check_var_size_nonblocking(u32 attributes, unsigned long size);
-
 #if IS_ENABLED(CONFIG_EFI_CAPSULE_LOADER)
 extern bool efi_capsule_pending(int *reset_type);