OSDev.org

How to perform protection (i386+,pmode) between tasks(segments) of the same privillege level?

[attachment deleted by admin]

Well for different task, keeps memory regions from one task out of the address space of a different task with the help of paging.

A possible advanced trick from my wizard-bag (might not work in every situation, though):

• have a supervisor component that is the one to choose which low-level component is active at a time
• when giving the access to one of these components, set its descriptor present bit on, leave other descriptors with present bit off.
• On context switchings between sub-tasks, toggle access bits ...

Now, this has a drawback : the supervisor component can virtually write anything to the table... potentially a protection flaw if not at DPL0 -- or you might have a system call for asking a trusted component to do the "present bit" switch for you ...

Now, this is a never-seen-anywhere-else-and-never-tried idea of mine ... so be wise when using it