Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!rutgers!dayton!ems!mark From: mark@ems.UUCP Newsgroups: comp.os.minix Subject: Re: MINIX memory management/protection Message-ID: <153@ems.UUCP> Date: Sun, 8-Feb-87 12:39:56 EST Article-I.D.: ems.153 Posted: Sun Feb 8 12:39:56 1987 Date-Received: Mon, 9-Feb-87 04:09:03 EST References: <252@hqda-ai.UUCP> <1169@steinmetz.steinmetz.UUCP> <511@bobkat.UUCP> <888@cartan.Berkeley.EDU> <299@netxcom.UUCP> Sender: news@ems.UUCP Reply-To: mark@ems.UUCP (Mark H. Colburn) Organization: EMS/McGraw-Hill, Eden Pairie, MN Lines: 33 Keywords: shared swapped jobs Summary: Are you sure you want to execute data? >>>In article <1169@steinmetz.steinmetz.UUCP> davidsen@kbsvax.UUCP (william E Davidsen) writes: >>>> >>>>If you allocate a full 64k to data, there is hardware protection: you >>>>can't address more than that. This assures that any program which >>>>doesn't deliberately set out to cause problems will not modify the >>>>code. ... >>> [ other comments deleted ] In article <299@netxcom.UUCP> beattie@netxcom.UUCP (Brian Beattie) writes: > >Actually if you arange your code so data follows (which MINIX does) >since all jumps/calls/rets (except the long vesion) are CS:OFFSET >you may jump into your data, but not outside of your process space. Are you really sure that you want to execute your data? Think about this for a minute. Who is to say what fun instructions you data would look like? Like, for example, it could change you CS:, DS:, ES: or SS: and then, even if it did nothing else, and (miraculously) returned back to the code in some kind of reasonable point, what is going to happen? Can you say that the program will not write outside of the process space? I can't, and I have seen this happen. There is no substitute for a hardware MMU. Do not underestimate the problems that executing data can produce. -- Mark H. Colburn mark@ems.uucp EMS/McGraw-Hill {rutgers|amdahl|ihnp4}!{dayton|meccts}!ems!mark 9855 West 78th Street Eden Prairie, MN 55344 (612) 829-8200 x235 -- Mark H. Colburn mark@ems.uucp EMS/McGraw-Hill {rutgers|amdahl|ihnp4}!{dayton|meccts}!ems!mark 9855 West 78th Street Eden Prairie, MN 55344 (612) 829-8200 x235