Is that in universal gcc, or OpenBSD only? Lance James -----Original Message----- From: Patrick Dolan [mailto:dolan@cc.admin.unt.edu] Sent: Wednesday, August 13, 2003 10:20 AM To: Eygene A. Ryabinkin Subject: Re: Buffer overflow prevention There is a flag for the Gnu C/C++ compilers, -fstack-protector, that will implement ProPolice stack protection. It should prevent stack smashing techniques. On Wednesday 13 August 2003 05:28 am, Eygene A. Ryabinkin wrote: > Hi! > I have an idea on buffer overflow prevention. I doubt that it's new, but I > haven't seen an implementation of it in any freely distributable Un*x > system. So, I hardly need your comments on it. > > Preliminary: I'm talking about Intel x86 architecture, but maybe it will > be applicable to others as well. > > The idea itself: all (correct me if I'm wrong) buffer overflows are based > on the fact that we're using the stack, referenced by SS:ESP pair, both for > procedure return address and for local variables. It seems to me, that > would we have two stacks -- one for real stack and one for variables -- it > will solve a bunch of problems. So, my suggestion: let us organise two > segments: one for normal stack, growing downwards, referenced by SS:ESP > pair and the second one, for local variables, referenced by GS:EBP pair, > with either upwards or downwards growing. Now, if we use first segment for > passing variables and procedure return addresses (normal stack usage), and > second segment only for local procedure variables, we will have the > following advantages: > 1) Local variables and return address will be physically (by means of CPU) > divided and it will not be possible to touch the return address by > overflowing local buffer. > 2) The procedure introduces only one extra register -- GS, since EBP is > very often used for the stack frame. > Of course, this two segments can be made non-executable, just in case. > > What we need to implement the idea: first, rewrite kernel to organise two > segments for every process and to place proper values into the segment > registers upon the program startup. Second, rewrite the compiler to support > the new scheme of local variables addresation. So, the changes are minimal, > in some sence. > > As I said, I hardly need your criticism, suggestions, etc. of any type. > rea -- Patrick Dolan UNT Information Security PGP ID: E5571154 Primary key fingerprint: 5681 25E4 6BE6 298E 9CF0 6F8D B13B 2456 E557 1154
