What’s the purpose of mmap memory protection PROT_NONE
I was reading the documentation of mmap and fell upon this line:
PROT_NONE Pages may not be accessed.
Is there any use to map a file to memory but never access it?
Answer
PROT_NONE can be used to implement guard pages, Microsoft has the same concept (MSDN).
To quote the first link:
... allocation of additional inaccessible memory during memory allocation operations is a technique for mitigating against exploitation of heap buffer overflows. These guard pages are unmapped pages placed between all memory allocations of one page or larger. The guard page causes a segmentation fault upon any access.
Thus useful in implementing protection for areas such as network interfacing, virtual machines, and interpreters. An example usage: pthread_attr_setguardsize, pthread_attr_getguardsize.