... >> The W^X implementation today is not complete. There exist many user level >> tricks that can be used to load and execute dynamic code. E.g., >> >> - Load the code into a file and map the file with R-X. >> >> - Load the code in an RW- page. Change the permissions to R--. Then, >> change the permissions to R-X. >> >> - Load the code in an RW- page. Remap the page with R-X to get a separate >> mapping to the same underlying physical page. >> >> IMO, these are all security holes as an attacker can exploit them to inject >> his own code. > > IMO, you are smoking crack^H^H very seriously misunderstanding what > W^X is supposed to protect from. > > W^X is not supposed to protect you from attackers that can already do > system calls. So loading code into a file then mapping the file as R-X > is in no way security hole in W^X. > > If you want to provide protection from attackers that _can_ do system > calls, fine, but please don't talk about W^X and please specify what > types of attacks you want to prevent and why that's good thing. > There are two things here - the idea behind W^X and the current realization of that idea in actual implementation. The idea behind W^X, as I understand, is to prevent a user from loading arbitrary code into a page and getting it to execute. If the user code contains a vulnerability, an attacker can exploit it to potentially inject his own code and get it to execute. This cannot be denied. >From that perspective, all of the above tricks I have mentioned are tricks that user code can use to load arbitrary code into a page and get it to execute. Now, I don't want the discussion to be stuck in a mere name. If what I am suggesting needs a name other than "W^X" in the opinion of the reviewers, that is fine with me. But I don't believe there is any disagreement that the above user tricks are security holes. Madhavan
