efi: pstore: Return proper errors on UEFI failures

Right now efi-pstore either returns 0 (success) or -EIO; but we
do have a function to convert UEFI errors in different standard
error codes, helping to narrow down potential issues more accurately.

So, let's use this helper here.
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/efi-pstore.c

@@ -136,7 +136,7 @@ static int efi_pstore_read_func(struct pstore_record *record,
 				     &size, record->buf);
 	if (status != EFI_SUCCESS) {
 		kfree(record->buf);
-		return -EIO;
+		return efi_status_to_err(status);
 	}
 
 	/*
@@ -189,7 +189,7 @@ static ssize_t efi_pstore_read(struct pstore_record *record)
 			return 0;
 
 		if (status != EFI_SUCCESS)
-			return -EIO;
+			return efi_status_to_err(status);
 
 		/* skip variables that don't concern us */
 		if (efi_guidcmp(guid, LINUX_EFI_CRASH_GUID))
@@ -227,7 +227,7 @@ static int efi_pstore_write(struct pstore_record *record)
 					    record->size, record->psi->buf,
 					    true);
 	efivar_unlock();
-	return status == EFI_SUCCESS ? 0 : -EIO;
+	return efi_status_to_err(status);
 };
 
 static int efi_pstore_erase(struct pstore_record *record)
@@ -238,7 +238,7 @@ static int efi_pstore_erase(struct pstore_record *record)
 				     PSTORE_EFI_ATTRIBUTES, 0, NULL);
 
 	if (status != EFI_SUCCESS && status != EFI_NOT_FOUND)
-		return -EIO;
+		return efi_status_to_err(status);
 	return 0;
 }