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VM_GROWSDOWN

VM_GROWSDOWN

Posted Aug 23, 2010 17:51 UTC (Mon) by PaXTeam (guest, #24616)
In reply to: VM_GROWSDOWN by foom
Parent article: An ancient kernel hole is closed

when talking about getting rid of VM_GROWSDOWN, it seems that people forget that it does not only expand the stack as needed, but it can also detect a kind of userland bug where the stack expansion request is beyond a certain architecture dependent limit (just look at the callers of expand_stack in the arch specific page fault handler and the checks before that). so statically allocating the initial task's stack range would let those bugs go undetected in the future. now admittedly this is a rare bug class (IIRC, gcc 2.96 had such a code generation bug) but it still means that there'll be a userland visible change when you get rid of VM_GROWSDOWN.


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