According to Chrétien’s translator D.D.R. Owen, this was the ointment which Mary Magdalene, Mary Salome, and Mary the mother of James procured to anoint the body of Christ (Jesus of Nazareth).
Their ointment obviously had excellent curative powers, for King Bagdemagus offered it for the wounds Lancelot sustained from crossing the Sword Bridge. As Owen points out, Bademagus having this (rather than, say, one of Morgan’s preparations) reinforces the echo of the Harrowing of Hell.