If you are trying to move or copy memory from PL addresses using the PS, then your standard mem* functions should work. They'll be slow and non-optimal, as others on the forums have noticed, but they should work. You can often adjust cache settings to speed these operations up.
If you are trying to use the PL to copy memory from one place in the DDR to another, then you might want to use a DMA of some type. A memset command could easily be made from a stream to memory DMA. memcmp could be done from two memory to stream DMAs. For open source examples of how you might build some of these functions, see this repo. Xilinx also provides official examples of functions such as these. Just beware of the bugs in Xilinx's stream to memory mapped (S2MM) design--they can be annoying to work around.