Correct, but in practice memory has permissions on a page level and most pages today are 4K. So a page containing a buffer is also likely to contain other data as well. Unless you are going to isolate each buffer by placing it in its own page.
That doesn't make sense to me. So an OS will assign a 4K page of memory to multiple processes, with some granularity that each process "should" only be able to write/read some of it?