As chrisseaton points out, you very much can change the permissions on a processes' memory at the page level. The mprotect system call lets you change the prote

As chrisseaton points out, you very much can change the permissions on a processes' memory at the page level. The mprotect system call lets you change the protection on regions of memory, but you can do fancy things by unmapping memory. A friend of mine from grad school did some really elaborate tricks related to memory protection to implement runtime systems for speculation ("Exploiting Coarse-Grain Speculative Parallelism", http://www.haripyla.com/wordpress/wp-content/uploads/2012/11/OOPSLA_2011.pdf http://www.haripyla.com/wordpress/wp-content/uploads/2012/11...) and deadlock elimination (see chapters 2 and 3 of his dissertation, "Safe Concurrent Programming and Execution", http://vtechworks.lib.vt.edu/bitstream/handle/10919/19276/Pyla_HK_D_2013.pdf?sequence=1 http://vtechworks.lib.vt.edu/bitstream/handle/10919/19276/Py...).