Electron–positron pair production at ultra-relativistic laser intensities has been one of the most interesting topics of high energy physics and plasma physics in the last several decades. Here we report simulations of copious electron–positron pair production via enhanced electron injection from a mass-limited foil driven by a circularly-polarized laser pulse focused to the forthcoming intensity of 1023 W cm–2. The laser pressure pushes the center foil forward as a whole with the lateral laser wave passing by the foil boundary and being reflected by the second thick carbon target. The accelerated electrons from the mass-limited foil are injected into the reflected laser wave in the hole-boring front of the carbon target, resulting in a significant enhancement of the γ-photon emission via nonlinear Compton scattering. Finally, we obtain 1014γ-photons with an average energy of 14.48 MeV and a conversion efficiency from the laser to the γ-ray energy of 18%. A dense beam of 1011 positrons is produced with an average energy of 160 MeV, which may have wide-range applications to astrophysics and fundamental physics.