Add personalization string callback to match description

crypto/fipsmodule/rand/entropy/entropy_sources.c

@@ -20,6 +20,13 @@ static int entropy_get_prediction_resistance(
   return 1;
 }
 
+static int entropy_get_personalization_string(
+  const struct entropy_source_t *entropy_source,
+  uint8_t personalization_string[CTR_DRBG_ENTROPY_LEN]) {
+  CRYPTO_sysrand(personalization_string, CTR_DRBG_ENTROPY_LEN);
+  return 1;
+}
+
 // - Tree DRBG with Jitter Entropy as root for seeding.
 // - OS as personalization string source.
 // - If run-time is on an Intel CPU and it supports rdrand, use it as a source
@@ -29,7 +36,7 @@ DEFINE_LOCAL_DATA(struct entropy_source_methods, tree_jitter_entropy_source_meth
   out->zeroize_thread = tree_jitter_zeroize_thread_drbg;
   out->free_thread = tree_jitter_free_thread_drbg;
   out->get_seed = tree_jitter_get_seed;
-  out->get_personalization_string = NULL;
+  out->get_personalization_string = entropy_get_personalization_string;
   if (have_fast_rdrand() == 1) {
     out->get_prediction_resistance = entropy_get_prediction_resistance;
   } else {