[PATCH v2] eficonfig: EFI_VARIABLE_APPEND_WRITE is not set for null key

[Masahisa Kojima]

The signed null key with authenticated header is used to clear
the PK, KEK, db and dbx. When CONFIG_EFI_MM_COMM_TEE is enabled
(StMM and OP-TEE based RPMB storage is used as the EFI variable
storage), clearing KEK, db and dbx by enrolling a signed null
key does not work as expected if EFI_VARIABLE_APPEND_WRITE
attritube is set.

This commit checks the selected file is null key, then
EFI_VARIABLE_APPEND_WRITE attibute will not be used for the null key.

Signed-off-by: Masahisa Kojima <masahisa.kojima at linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
Changes in v2:
- s/size == 0/!size/

 cmd/eficonfig_sbkey.c | 40 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/cmd/eficonfig_sbkey.c b/cmd/eficonfig_sbkey.c
index 6e0bebf1d4..7fb0467543 100644
--- a/cmd/eficonfig_sbkey.c
+++ b/cmd/eficonfig_sbkey.c
@@ -72,6 +72,30 @@ static bool file_have_auth_header(void *buf, efi_uintn_t size)
 	return true;
 }
 
+/**
+ * file_is_null_key() - check the file is an authenticated and signed null key
+ * @auth:	pointer to the file
+ * @size:	file size
+ * @null_key:	pointer to store the result
+ * Return:	status code
+ */
+static efi_status_t file_is_null_key(struct efi_variable_authentication_2 *auth,
+				     efi_uintn_t size, bool *null_key)
+{
+	efi_status_t ret = EFI_SUCCESS;
+
+	if (size < (sizeof(auth->time_stamp) + auth->auth_info.hdr.dwLength))
+		return EFI_INVALID_PARAMETER;
+
+	size -= (sizeof(auth->time_stamp) + auth->auth_info.hdr.dwLength);
+	if (!size) /* No payload */
+		*null_key = true;
+	else
+		*null_key = false;
+
+	return ret;
+}
+
 /**
  * eficonfig_process_enroll_key() - enroll key into signature database
  *
@@ -84,6 +108,7 @@ static efi_status_t eficonfig_process_enroll_key(void *data)
 	char *buf = NULL;
 	efi_uintn_t size;
 	efi_status_t ret;
+	bool null_key = false;
 	struct efi_file_handle *f = NULL;
 	struct efi_device_path *full_dp = NULL;
 	struct eficonfig_select_file_info file_info;
@@ -149,13 +174,24 @@ static efi_status_t eficonfig_process_enroll_key(void *data)
 		goto out;
 	}
 
+	ret = file_is_null_key((struct efi_variable_authentication_2 *)buf,
+			       size, &null_key);
+	if (ret != EFI_SUCCESS) {
+		eficonfig_print_msg("ERROR! Invalid file format.");
+		goto out;
+	}
+
 	attr = EFI_VARIABLE_NON_VOLATILE |
 	       EFI_VARIABLE_BOOTSERVICE_ACCESS |
 	       EFI_VARIABLE_RUNTIME_ACCESS |
 	       EFI_VARIABLE_TIME_BASED_AUTHENTICATED_WRITE_ACCESS;
 
-	/* PK can enroll only one certificate */
-	if (u16_strcmp(data, u"PK")) {
+	/*
+	 * PK can enroll only one certificate.
+	 * The signed null key is used to clear KEK, db and dbx.
+	 * EFI_VARIABLE_APPEND_WRITE attribute must not be set in these cases.
+	 */
+	if (u16_strcmp(data, u"PK") && !null_key) {
 		efi_uintn_t db_size = 0;
 
 		/* check the variable exists. If exists, add APPEND_WRITE attribute */
-- 
2.17.1