remove feature probe

CMakeLists.txt

@@ -476,16 +476,6 @@ if(PLATFORM_SUPPORTS_KTLS)
     target_compile_options(${PROJECT_NAME} PUBLIC -DS2N_PLATFORM_SUPPORTS_KTLS)
 endif()
 
-try_compile(
-        LIBCRYPTO_SUPPORTS_TLS_PRF
-        ${CMAKE_BINARY_DIR}
-        SOURCES "${CMAKE_CURRENT_LIST_DIR}/tests/features/tls_prf.c"
-        LINK_LIBRARIES ${LINK_LIB} ${OS_LIBS}
-)
-if(LIBCRYPTO_SUPPORTS_TLS_PRF)
-    target_compile_options(${PROJECT_NAME} PUBLIC -DS2N_LIBCRYPTO_SUPPORTS_TLS_PRF)
-endif()
-
 if (NOT DEFINED CMAKE_AR)
 	message(STATUS "CMAKE_AR undefined, setting to `ar` by default")
 	SET(CMAKE_AR ar)

s2n.mk

@@ -261,12 +261,6 @@ ifeq ($(TRY_COMPILE_KTLS), 0)
 	DEFAULT_CFLAGS += -DS2N_PLATFORM_SUPPORTS_KTLS
 endif
 
-# Determine if libcrypto PRF implementation is available
-TRY_COMPILE_TLS_PRF := $(call try_compile,$(S2N_ROOT)/tests/features/tls_prf.c)
-ifeq ($(TRY_COMPILE_TLS_PRF), 0)
-	DEFAULT_CFLAGS += -DS2N_LIBCRYPTO_SUPPORTS_TLS_PRF
-endif
-
 CFLAGS_LLVM = ${DEFAULT_CFLAGS} -emit-llvm -c -g -O1
 
 $(BITCODE_DIR)%.bc: %.c

tests/unit/s2n_tls_prf_test.c

@@ -313,17 +313,11 @@ int main(int argc, char **argv)
         };
     };
 
-    /* Ensure that the feature probe properly indicates support for the libcrypto TLS PRF API */
-    {
-        /* The libcrypto TLS PRF feature probe should succeed for all AWSLC versions */
-        if (s2n_libcrypto_is_awslc()) {
-            EXPECT_TRUE(s2n_libcrypto_supports_tls_prf());
-        }
-
-        /* The libcrypto TLS PRF feature probe should fail for non-AWSLC/BoringSSL libcryptos */
-        if (!s2n_libcrypto_is_awslc() && !s2n_libcrypto_is_boringssl()) {
-            EXPECT_FALSE(s2n_libcrypto_supports_tls_prf());
-        }
+    /* Ensure that the libcrypto TLS PRF API is only enabled for AWSLC */
+    if (s2n_libcrypto_is_awslc()) {
+        EXPECT_TRUE(s2n_libcrypto_supports_tls_prf());
+    } else {
+        EXPECT_FALSE(s2n_libcrypto_supports_tls_prf());
     }
 
     /* s2n_prf tests */

tls/s2n_prf.c

@@ -463,7 +463,7 @@ S2N_RESULT s2n_prf_free(struct s2n_connection *conn)
 
 bool s2n_libcrypto_supports_tls_prf()
 {
-#ifdef S2N_LIBCRYPTO_SUPPORTS_TLS_PRF
+#if S2N_LIBCRYPTO_SUPPORTS_TLS_PRF
     return true;
 #else
     return false;
@@ -497,7 +497,7 @@ S2N_RESULT s2n_custom_prf(struct s2n_connection *conn, struct s2n_blob *secret,
     return S2N_RESULT_OK;
 }
 
-#ifdef S2N_LIBCRYPTO_SUPPORTS_TLS_PRF
+#if S2N_LIBCRYPTO_SUPPORTS_TLS_PRF
 
 /* The AWSLC TLS PRF API is exported in all AWSLC versions. However, in the AWSLC FIPS branch, this
  * API is defined in a private header:

tls/s2n_prf.h

@@ -25,6 +25,12 @@
 /* Enough to support TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384, 2*SHA384_DIGEST_LEN + 2*AES256_KEY_SIZE */
 #define S2N_MAX_KEY_BLOCK_LEN 160
 
+#if defined(OPENSSL_IS_AWSLC)
+    #define S2N_LIBCRYPTO_SUPPORTS_TLS_PRF 1
+#else
+    #define S2N_LIBCRYPTO_SUPPORTS_TLS_PRF 0
+#endif
+
 union p_hash_state {
     struct s2n_hmac_state s2n_hmac;
     struct s2n_evp_hmac_state evp_hmac;