Make field required with lightning:inputField and lightning:recordEditForm

OOTB, lightning:inputfield handles field validations that are configured through your object's field settings, so that would be the first place you want to check in order to make your fields "required".

If for whatever reason, the above is not an option (eventhough it should be), then adding an aura:id that identifies all your lighting:inputfield fields will enable you to simply 'fetch' all of them with component.find('yourAuraId') which returns an array you can iterate over to perform your field validations.

You can then bind your validation method to the onsubmit event and do a simple check for blank fields:

isFormValid: function (cmp, evt, helper) {
    const requiredFields = cmp.find('yourAuraId') || [];
    var isValid = true;
    requiredFields.forEach(e => {
        if (e.get('v.value')=='' || e.get('v.value').trim().length==0 ) {
            isValid = false;
        }
    });

    return isValid;
},

based on the what is returned by the validation method, you can proceed with submitting the form or not with event.preventDefault(); // stop the form from submitting

Winter20 , required attribute available for lightning:inputField from winter 20