Add warnings to test code and data about storage format stability

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

scripts/mbedtls_dev/psa_storage.py

@@ -1,4 +1,9 @@
 """Knowledge about the PSA key store as implemented in Mbed TLS.
+
+Note that if you need to make a change that affects how keys are
+stored, this may indicate that the key store is changing in a
+backward-incompatible way! Think carefully about backward compatibility
+before changing how test data is constructed or validated.
 """
 
 # Copyright The Mbed TLS Contributors
@@ -146,6 +151,11 @@ class Key:
         This is the content of the PSA storage file. When PSA storage is
         implemented over stdio files, this does not include any wrapping made
         by the PSA-storage-over-stdio-file implementation.
+
+        Note that if you need to make a change in this function,
+        this may indicate that the key store is changing in a
+        backward-incompatible way! Think carefully about backward
+        compatibility before making any change here.
         """
         header = self.MAGIC + self.pack('L', self.version)
         if self.version == 0:

tests/suites/test_suite_psa_crypto_persistent_key.data

@@ -1,3 +1,8 @@
+# Note that if you need to make a change that affects how keys are
+# stored, this may indicate that the key store is changing in a
+# backward-incompatible way! Think carefully about backward compatibility
+# before changing how test data is constructed or validated.
+
 Format for storage: RSA private key
 format_storage_data_check:"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":"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":PSA_KEY_LIFETIME_PERSISTENT:PSA_KEY_TYPE_RSA_KEY_PAIR:1024:PSA_KEY_USAGE_EXPORT:PSA_ALG_CATEGORY_ASYMMETRIC_ENCRYPTION:PSA_ALG_CATEGORY_SIGN
 

tests/suites/test_suite_psa_crypto_persistent_key.function

@@ -5,6 +5,11 @@
  * on the the storage format. On the other hand, these tests treat the storage
  * subsystem as a black box, and in particular have no reliance on the
  * internals of the ITS implementation.
+ *
+ * Note that if you need to make a change that affects how files are
+ * stored, this may indicate that the key store is changing in a
+ * backward-incompatible way! Think carefully about backward compatibility
+ * before changing how test data is constructed or validated.
  */
 
 #include <stdint.h>

tests/suites/test_suite_psa_its.function

@@ -3,6 +3,11 @@
 /* This test file is specific to the ITS implementation in PSA Crypto
  * on top of stdio. It expects to know what the stdio name of a file is
  * based on its keystore name.
+ *
+ * Note that if you need to make a change that affects how files are
+ * stored, this may indicate that the key store is changing in a
+ * backward-incompatible way! Think carefully about backward compatibility
+ * before changing how test data is constructed or validated.
  */
 
 #include "../library/psa_crypto_its.h"