Protected Memory...

Hi all,

I've been looking around and I cant find a definite answer: do all BSD systems support protected memory or is it just the off few like OSX and OpenBSD.

This is really just a curiosity thing; I've recently become interested in the nuts and bolts of the OS .

If anyone could point me in the direction of some interesting info about BSD I'd be very interested.

Thanks,

Mark.

Do you mean noexec heap/stack when you say "protected memory"? I believe that Net/Free/Open BSDs (and even Linux) all do it where the architecture explicitly supports fine grained flagging of memory (e.g.) in the AMD64, PowerPC, SPARC, SPARC64, Alpha, hppa etc. Not all of them do it in all the architectures, so your mileage may vary, but OpenBSD/NetBSD do all of the above and I'm pretty certain all the AMD64 implementations do it. OpenBSD also does it in i386 with making a few compromises (since the i386 architecture doesn't really support fine grained support of noexec bit on memory). By fine-grained, I mean, the processor supports that different pages of memory can be flagged executable or not. i386 does it in a very limited way (i.e.) you can indicate that anything below address X is executable and anything above it isn't, but not individual pages. Hence, OpenBSD had to do lots of dancing around with how the loader places the stack in memory with the i386 port to achieve this (the heap isn't non-exec on i386). There are also some architectures that don't support any kind of noexec bit, so obviously the OSs can't do any protection here.

Here's some further links:
http://www.openbsd.org/papers/auug04/index.html
http://marc.theaimsgroup.com/?l=ope...64918210103&w=2
http://www.netbsd.org/Documentation...l/non-exec.html

Thanks a lot scorp' that really did help me a lot .

Mark.