Merge pull request #812 from antonio-nino-diaz-arm/an/clear-static-vars

Clear static variables in X509 parser on error

1 files changed, 37 insertions, 2 deletions

diff --git a/drivers/auth/mbedtls/mbedtls_x509_parser.c b/drivers/auth/mbedtls/mbedtls_x509_parser.c
index 1a6a9a75..73da9d1e 100644
--- a/drivers/auth/mbedtls/mbedtls_x509_parser.c
+++ b/drivers/auth/mbedtls/mbedtls_x509_parser.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2017, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -36,6 +36,7 @@
  * extensions field, such as an image hash or a public key.
  */
 
+#include <arch_helpers.h>
 #include <assert.h>
 #include <img_parser_mod.h>
 #include <mbedtls_common.h>
@@ -64,6 +65,26 @@ static mbedtls_asn1_buf sig_alg;
 static mbedtls_asn1_buf signature;
 
 /*
+ * Clear all static temporary variables.
+ */
+static void clear_temp_vars(void)
+{
+#define ZERO_AND_CLEAN(x)					\
+	do {							\
+		memset(&x, 0, sizeof(x));			\
+		clean_dcache_range((uintptr_t)&x, sizeof(x));	\
+	} while (0);
+
+	ZERO_AND_CLEAN(tbs)
+	ZERO_AND_CLEAN(v3_ext);
+	ZERO_AND_CLEAN(pk);
+	ZERO_AND_CLEAN(sig_alg);
+	ZERO_AND_CLEAN(signature);
+
+#undef ZERO_AND_CLEAN
+}
+
+/*
  * Get X509v3 extension
  *
  * Global variable 'v3_ext' must point to the extensions region
@@ -134,7 +155,12 @@ static int get_ext(const char *oid, void **ext, unsigned int *ext_len)
 
 /*
  * Check the integrity of the certificate ASN.1 structure.
+ *
  * Extract the relevant data that will be used later during authentication.
+ *
+ * This function doesn't clear the static variables located on the top of this
+ * file in case of an error. It is only called from check_integrity(), which
+ * performs the cleanup if necessary.
  */
 static int cert_parse(void *img, unsigned int img_len)
 {
@@ -398,9 +424,18 @@ static void init(void)
 	mbedtls_init();
 }
 
+/*
+ * Wrapper for cert_parse() that clears the static variables used by it in case
+ * of an error.
+ */
 static int check_integrity(void *img, unsigned int img_len)
 {
-	return cert_parse(img, img_len);
+	int rc = cert_parse(img, img_len);
+
+	if (rc != IMG_PARSER_OK)
+		clear_temp_vars();
+
+	return rc;
 }
 
 /*