PSA test case generation: dependency inference class: key not supported

In `psa_test_case.TestCase`, add a method `assumes_not_supported` which
allows using the automatic dependency calculation framework when the test
case intends to run in configurations where one mechanism is not supported.

Use `psa_test_case.TestCase` for not-supported test cases for key import and
generation.

No change to the generated output.

Signed-off-by: Gilles Peskine <[email protected]>

scripts/generate_psa_tests.py

@@ -26,7 +26,7 @@ from mbedtls_framework import test_data_generation
 
 def test_case_for_key_type_not_supported(
         verb: str, key_type: str, bits: int,
-        dependencies: List[str],
+        not_supported_mechanism: str,
         *args: str,
         param_descr: str = ''
 ) -> test_case.TestCase:
@@ -35,17 +35,16 @@ def test_case_for_key_type_not_supported(
     """
     tc = psa_test_case.TestCase()
     short_key_type = crypto_knowledge.short_expression(key_type)
-    adverb = 'not' if dependencies else 'never'
-    if param_descr:
-        adverb = param_descr + ' ' + adverb
-    tc.set_description('PSA {} {} {}-bit {} supported'
-                       .format(verb, short_key_type, bits, adverb))
+    tc.set_description('PSA {} {} {}-bit{} not supported'
+                       .format(verb, short_key_type, bits,
+                               ' ' + param_descr if param_descr else ''))
+    # if tc.description == 'PSA import RSA_KEY_PAIR 1024-bit not supported':
+    #     import pdb; pdb.set_trace()
     tc.set_function(verb + '_not_supported')
     tc.set_key_bits(bits)
     tc.set_key_pair_usage([verb.upper()])
+    tc.assumes_not_supported(not_supported_mechanism)
     tc.set_arguments([key_type] + list(args))
-    tc.set_dependencies(dependencies)
-    tc.skip_if_any_not_implemented(dependencies)
     return tc
 
 class KeyTypeNotSupported:
@@ -77,39 +76,27 @@ class KeyTypeNotSupported:
             # Don't generate test cases for key types that are always supported.
             # They would be skipped in all configurations, which is noise.
             return
-        import_dependencies = [('!' if param is None else '') +
-                               psa_information.psa_want_symbol(kt.name)]
-        if kt.params is not None:
-            import_dependencies += [('!' if param == i else '') +
-                                    psa_information.psa_want_symbol(sym)
-                                    for i, sym in enumerate(kt.params)]
-        if kt.name.endswith('_PUBLIC_KEY'):
-            generate_dependencies = []
+        if param is None:
+            not_supported_mechanism = kt.name
         else:
-            generate_dependencies = \
-                psa_information.fix_key_pair_dependencies(import_dependencies,
-                                                          ['GENERATE'])
-            import_dependencies = \
-                psa_information.fix_key_pair_dependencies(import_dependencies,
-                                                          ['IMPORT'])
+            assert kt.params is not None
+            not_supported_mechanism = kt.params[param]
         for bits in kt.sizes_to_test():
             yield test_case_for_key_type_not_supported(
                 'import', kt.expression, bits,
-                psa_information.finish_family_dependencies(import_dependencies, bits),
+                not_supported_mechanism,
                 test_case.hex_string(kt.key_material(bits)),
                 param_descr=param_descr,
             )
-            if not generate_dependencies and param is not None:
-                # If generation is impossible for this key type, rather than
-                # supported or not depending on implementation capabilities,
-                # only generate the test case once.
-                continue
-                # For public key we expect that key generation fails with
-                # INVALID_ARGUMENT. It is handled by KeyGenerate class.
+            # Don't generate not-supported test cases for key generation of
+            # public keys. Our implementation always returns
+            # PSA_ERROR_INVALID_ARGUMENT when attempting to generate a
+            # public key, so we cover this together with the positive cases
+            # in the KeyGenerate class.
             if not kt.is_public():
                 yield test_case_for_key_type_not_supported(
                     'generate', kt.expression, bits,
-                    psa_information.finish_family_dependencies(generate_dependencies, bits),
+                    not_supported_mechanism,
                     str(bits),
                     param_descr=param_descr,
                 )

scripts/mbedtls_framework/psa_test_case.py

@@ -70,6 +70,7 @@ class TestCase(test_case.TestCase):
         self.manual_dependencies = [] #type: List[str]
         self.automatic_dependencies = set() #type: Set[str]
         self.dependency_prefix = dependency_prefix #type: Optional[str]
+        self.negated_dependencies = set() #type: Set[str]
         self.key_bits = None #type: Optional[int]
         self.key_pair_usage = None #type: Optional[List[str]]
 
@@ -104,16 +105,56 @@ class TestCase(test_case.TestCase):
             dependencies = psa_information.fix_key_pair_dependencies(dependencies,
                                                                      self.key_pair_usage)
         if 'PSA_WANT_KEY_TYPE_RSA_KEY_PAIR_GENERATE' in dependencies and \
+           'PSA_WANT_KEY_TYPE_RSA_KEY_PAIR_GENERATE' not in self.negated_dependencies and \
            self.key_bits is not None:
             size_dependency = ('PSA_VENDOR_RSA_GENERATE_MIN_KEY_BITS <= ' +
                                str(self.key_bits))
             dependencies.append(size_dependency)
         return dependencies
 
+    def assumes_not_supported(self, name: str) -> None:
+        """Negate the given mechanism for automatic dependency generation.
+
+        Call this function before set_arguments() for a test case that should
+        run if the given mechanism is not supported.
+
+        Call modifiers such as set_key_bits() and set_key_pair_usage() before
+        calling this method, if applicable.
+
+        A mechanism is a PSA_XXX symbol, e.g. PSA_KEY_TYPE_AES, PSA_ALG_HMAC,
+        etc. For mechanisms like ECC curves where the support status includes
+        the key bit-size, this class assumes that only one bit-size is
+        involved in a given test case.
+        """
+        if name == 'PSA_KEY_TYPE_RSA_KEY_PAIR' and \
+           self.key_bits is not None and \
+           self.key_pair_usage == ['GENERATE']:
+            # When RSA key pair generation is not supported, it could be
+            # due to the specific key size is out of range, or because
+            # RSA key pair generation itself is not supported. Assume the
+            # latter.
+            dep = psa_information.psa_want_symbol(name, prefix=self.dependency_prefix)
+
+            self.negated_dependencies.add(dep + '_GENERATE')
+            return
+        dependencies = self.infer_dependencies([name])
+        # * If we have more than one dependency to negate, the result would
+        #   say that all of the dependencies are disabled, which is not
+        #   a desirable outcome: the negation of (A and B) is (!A or !B),
+        #   not (!A and !B).
+        # * If we have no dependency to negate, the result wouldn't be a
+        #   not-supported case.
+        # Assert that we don't reach either such case.
+        assert len(dependencies) == 1
+        self.negated_dependencies.add(dependencies[0])
+
     def set_arguments(self, arguments: List[str]) -> None:
         """Set test case arguments and automatically infer dependencies."""
         super().set_arguments(arguments)
         dependencies = self.infer_dependencies(arguments)
+        for i in range(len(dependencies)): #pylint: disable=consider-using-enumerate
+            if dependencies[i] in self.negated_dependencies:
+                dependencies[i] = '!' + dependencies[i]
         self.skip_if_any_not_implemented(dependencies)
         self.automatic_dependencies.update(dependencies)