Landsat 8 L1 products are "Terrain Corrected",
that said it means that are they already "topographically corrected", like both words are synonyms or you need to apply correction techniques as well? (eg i.topo.corr for Grass)
According to section 10.2 Level 1 Algorithms from NASA's Landsat 7 Science Data Users Handbook, all Landsat 7 Level 1T products are corrected for terrain effects (see also Figure 10.4). The same applies for Landsat 8 data of level 1T which refers to Standard Terrain Correction (Level 1T).
The correction(s) might not be perfect. Thus, one can, in theory, undergo a more detailed process for ortho-rectifying Landsat L1G products by using a DEM of higher resolution/quality than the well known DEMs SRTM or/and ASTER GDEM(2) both of which can be considered, depending on the application, as being coarse.