  This paper investigates the integration of a reconfigurable intelligent
surface (RIS) into a secure multiuser massive multiple-input multiple-output
(MIMO) system in the presence of transceiver hardware impairments (HWI),
imperfect channel state information (CSI), and spatially correlated channels.
We first introduce a linear minimum-mean-square error estimation algorithm for
the aggregate channel by considering the impact of transceiver HWI and RIS
phase-shift errors. Then, we derive a lower bound for the achievable ergodic
secrecy rate in the presence of a multi-antenna eavesdropper when artificial
noise (AN) is employed at the base station (BS). In addition, the obtained
expressions of the ergodic secrecy rate are further simplified in some
noteworthy special cases to obtain valuable insights. To counteract the effects
of HWI, we present a power allocation optimization strategy between the
confidential signals and AN, which admits a fixed-point equation solution. Our
analysis reveals that a non-zero ergodic secrecy rate is preserved if the total
transmit power decreases no faster than $1/N$, where $N$ is the number of RIS
elements. Moreover, the ergodic secrecy rate grows logarithmically with the
number of BS antennas $M$ and approaches a certain limit in the asymptotic
regime $N\rightarrow\infty$. Simulation results are provided to verify the
derived analytical results. They reveal the impact of key design parameters on
the secrecy rate. It is shown that, with the proposed power allocation
strategy, the secrecy rate loss due to HWI can be counteracted by increasing
the number of low-cost RIS elements.
