As reported by fanjinke51@yeah.net

http://mail.openjdk.java.net/pipermail/hotspot-dev/2019-April/037725.html

We have:

const char* VM_Version_Ext::cpu_family_description(void) {
  int cpu_family_id = extended_cpu_family();
  if (is_amd()) {
    return _family_id_amd[cpu_family_id];
  }
  if (is_intel()) {
    if (cpu_family_id == CPU_FAMILY_PENTIUMPRO) {
      return cpu_model_description();
    }
    return _family_id_intel[cpu_family_id];
  }
  if (is_hygon()) {
    return "Dhyana";
  }

  return "Unknown x86";
}

which indexes into the _family_id_xx arrays using the value returned by extended_cpu_family(). But there is no check that the index is within range as can happen with newer processes. For example AMD Zen will have an id of decimal 23, but the _family_id_amd array only has 17 entries.

We need to add new entries for AMD Zen and ensure no out-of-bound accesses.