A página do manual descreve o significado dos VmFlags:
The "VmFlags" line (available since Linux 3.8) represents
the kernel flags associated with the virtual memory area,
encoded using the following two-letter codes:
rd - readable
wr - writable
ex - executable
sh - shared
mr - may read
mw - may write
me - may execute
ms - may share
Qual é a diferença entre "readable" e "may read"? Parecem equivalentes. O mesmo para as versões write/executable/share.