Re: Non-Exec stack patches

From: David Mosberger
Date: Wed Mar 24 2004 - 14:19:07 EST

>>>>> On Wed, 24 Mar 2004 11:02:45 -0800, John Reiser <jreiser@xxxxxxxxxxxx> said:

>> Only one mprotect() call is needed to make the entire stack
>> executable.

John> mprotect() only works on the portion that is currently allocated.
John> If the stack grows, then another call is needed.

No, mprotect() on the entire stack will mark the vm_area with the
desired protection and VM_GROWSDOWN/VM_GROWSUP will expand
automatically with the new protection. And if you want to expand the
stack in user-level, e.g., by intercepting SIGSEGV, you'll either do
an mmap() or mprotect() at any rate so there is zero extra cost there.

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