Fix boolean options in the wrong section

Boolean options that modify the behavior of a module are supposed to be in
the "feature support" section, not in the "configuration options" support:
that section is documented to contain commented-out definitions with a
value, for which the comment contains the default version. In particular,
merely uncommenting a definition in the "configuration options" section is
not supposed to change anything.

Move the offending boolean options to the proper section.

This causes those options to be enabled by `config.py full` unless
explicitly excluded. For the moved options:

* Everest is already explicitly excluded.
* The ALT options need to link against a custom function, so exclude them.
* `MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE` is ok for testing, and is
  currently never tested in `all.sh`. With this commit, we will now test the
  library with it enabled in configurations based on `full`.

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

include/mbedtls/config.h

@@ -265,6 +265,45 @@
 //#define MBEDTLS_PLATFORM_NV_SEED_ALT
 //#define MBEDTLS_PLATFORM_SETUP_TEARDOWN_ALT
 
+/**
+ * Uncomment the macro to let Mbed TLS use your alternate implementation of
+ * mbedtls_platform_gmtime_r(). This replaces the default implementation in
+ * platform_util.c.
+ *
+ * gmtime() is not a thread-safe function as defined in the C standard. The
+ * library will try to use safer implementations of this function, such as
+ * gmtime_r() when available. However, if Mbed TLS cannot identify the target
+ * system, the implementation of mbedtls_platform_gmtime_r() will default to
+ * using the standard gmtime(). In this case, calls from the library to
+ * gmtime() will be guarded by the global mutex mbedtls_threading_gmtime_mutex
+ * if MBEDTLS_THREADING_C is enabled. We recommend that calls from outside the
+ * library are also guarded with this mutex to avoid race conditions. However,
+ * if the macro MBEDTLS_PLATFORM_GMTIME_R_ALT is defined, Mbed TLS will
+ * unconditionally use the implementation for mbedtls_platform_gmtime_r()
+ * supplied at compile time.
+ */
+//#define MBEDTLS_PLATFORM_GMTIME_R_ALT
+
+/**
+ * Uncomment the macro to let mbed TLS use your alternate implementation of
+ * mbedtls_platform_zeroize(). This replaces the default implementation in
+ * platform_util.c.
+ *
+ * mbedtls_platform_zeroize() is a widely used function across the library to
+ * zero a block of memory. The implementation is expected to be secure in the
+ * sense that it has been written to prevent the compiler from removing calls
+ * to mbedtls_platform_zeroize() as part of redundant code elimination
+ * optimizations. However, it is difficult to guarantee that calls to
+ * mbedtls_platform_zeroize() will not be optimized by the compiler as older
+ * versions of the C language standards do not provide a secure implementation
+ * of memset(). Therefore, MBEDTLS_PLATFORM_ZEROIZE_ALT enables users to
+ * configure their own implementation of mbedtls_platform_zeroize(), for
+ * example by using directives specific to their compiler, features from newer
+ * C standards (e.g using memset_s() in C11) or calling a secure memset() from
+ * their system (e.g explicit_bzero() in BSD).
+ */
+//#define MBEDTLS_PLATFORM_ZEROIZE_ALT
+
 /**
  * \def MBEDTLS_DEPRECATED_WARNING
  *
@@ -818,6 +857,15 @@
  */
 #define MBEDTLS_REMOVE_3DES_CIPHERSUITES
 
+/**
+ * Enable the verified implementations of ECDH primitives from Project Everest
+ * (currently only Curve25519). This feature changes the layout of ECDH
+ * contexts and therefore is a compatibility break for applications that access
+ * fields of a mbedtls_ecdh_context structure directly. See also
+ * MBEDTLS_ECDH_LEGACY_CONTEXT in include/mbedtls/ecdh.h.
+ */
+//#define MBEDTLS_ECDH_VARIANT_EVEREST_ENABLED
+
 /**
  * \def MBEDTLS_ECP_DP_SECP192R1_ENABLED
  *
@@ -2117,6 +2165,23 @@
  */
 //#define MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH
 
+/**
+ * Allow SHA-1 in the default TLS configuration for TLS 1.2 handshake
+ * signature and ciphersuite selection. Without this build-time option, SHA-1
+ * support must be activated explicitly through mbedtls_ssl_conf_sig_hashes.
+ * The use of SHA-1 in TLS <= 1.1 and in HMAC-SHA-1 is always allowed by
+ * default. At the time of writing, there is no practical attack on the use
+ * of SHA-1 in handshake signatures, hence this option is turned on by default
+ * to preserve compatibility with existing peers, but the general
+ * warning applies nonetheless:
+ *
+ * \warning   SHA-1 is considered a weak message digest and its use constitutes
+ *            a security risk. If possible, we recommend avoiding dependencies
+ *            on it, and considering stronger message digests instead.
+ *
+ */
+//#define MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE
+
 /**
  * \def MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN
  *
@@ -4141,71 +4206,6 @@
 //#define MBEDTLS_X509_MAX_INTERMEDIATE_CA   8   /**< Maximum number of intermediate CAs in a verification chain. */
 //#define MBEDTLS_X509_MAX_FILE_PATH_LEN     512 /**< Maximum length of a path/filename string in bytes including the null terminator character ('\0'). */
 
-/**
- * Allow SHA-1 in the default TLS configuration for TLS 1.2 handshake
- * signature and ciphersuite selection. Without this build-time option, SHA-1
- * support must be activated explicitly through mbedtls_ssl_conf_sig_hashes.
- * The use of SHA-1 in TLS <= 1.1 and in HMAC-SHA-1 is always allowed by
- * default. At the time of writing, there is no practical attack on the use
- * of SHA-1 in handshake signatures, hence this option is turned on by default
- * to preserve compatibility with existing peers, but the general
- * warning applies nonetheless:
- *
- * \warning   SHA-1 is considered a weak message digest and its use constitutes
- *            a security risk. If possible, we recommend avoiding dependencies
- *            on it, and considering stronger message digests instead.
- *
- */
-//#define MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE
-
-/**
- * Uncomment the macro to let mbed TLS use your alternate implementation of
- * mbedtls_platform_zeroize(). This replaces the default implementation in
- * platform_util.c.
- *
- * mbedtls_platform_zeroize() is a widely used function across the library to
- * zero a block of memory. The implementation is expected to be secure in the
- * sense that it has been written to prevent the compiler from removing calls
- * to mbedtls_platform_zeroize() as part of redundant code elimination
- * optimizations. However, it is difficult to guarantee that calls to
- * mbedtls_platform_zeroize() will not be optimized by the compiler as older
- * versions of the C language standards do not provide a secure implementation
- * of memset(). Therefore, MBEDTLS_PLATFORM_ZEROIZE_ALT enables users to
- * configure their own implementation of mbedtls_platform_zeroize(), for
- * example by using directives specific to their compiler, features from newer
- * C standards (e.g using memset_s() in C11) or calling a secure memset() from
- * their system (e.g explicit_bzero() in BSD).
- */
-//#define MBEDTLS_PLATFORM_ZEROIZE_ALT
-
-/**
- * Uncomment the macro to let Mbed TLS use your alternate implementation of
- * mbedtls_platform_gmtime_r(). This replaces the default implementation in
- * platform_util.c.
- *
- * gmtime() is not a thread-safe function as defined in the C standard. The
- * library will try to use safer implementations of this function, such as
- * gmtime_r() when available. However, if Mbed TLS cannot identify the target
- * system, the implementation of mbedtls_platform_gmtime_r() will default to
- * using the standard gmtime(). In this case, calls from the library to
- * gmtime() will be guarded by the global mutex mbedtls_threading_gmtime_mutex
- * if MBEDTLS_THREADING_C is enabled. We recommend that calls from outside the
- * library are also guarded with this mutex to avoid race conditions. However,
- * if the macro MBEDTLS_PLATFORM_GMTIME_R_ALT is defined, Mbed TLS will
- * unconditionally use the implementation for mbedtls_platform_gmtime_r()
- * supplied at compile time.
- */
-//#define MBEDTLS_PLATFORM_GMTIME_R_ALT
-
-/**
- * Enable the verified implementations of ECDH primitives from Project Everest
- * (currently only Curve25519). This feature changes the layout of ECDH
- * contexts and therefore is a compatibility break for applications that access
- * fields of a mbedtls_ecdh_context structure directly. See also
- * MBEDTLS_ECDH_LEGACY_CONTEXT in include/mbedtls/ecdh.h.
- */
-//#define MBEDTLS_ECDH_VARIANT_EVEREST_ENABLED
-
 /** \} name SECTION: Module configuration options */
 
 /* Target and application specific configurations

scripts/config.py

@@ -225,7 +225,11 @@ def is_seamless_alt(name):
     Exclude alternative implementations of library functions since they require
     an implementation of the relevant functions and an xxx_alt.h header.
     """
-    if name == 'MBEDTLS_PLATFORM_SETUP_TEARDOWN_ALT':
+    if name in (
+        'MBEDTLS_PLATFORM_GMTIME_R_ALT',
+        'MBEDTLS_PLATFORM_SETUP_TEARDOWN_ALT',
+        'MBEDTLS_PLATFORM_ZEROIZE_ALT',
+    ):
         # Similar to non-platform xxx_ALT, requires platform_alt.h
         return False
     return name.startswith('MBEDTLS_PLATFORM_')