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Michael Cohen Scott Lawrence wrote:
What exactly is SDL, and why would any terminal-based programs use it? Can you get us trustworthy benchmarks? On 12/29/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote:NaCl seems to be working as a sandbox. The only thing that you need to do that is strange with it is compile with sdl=none (this disables SDL) so that the programs can't make graphical windows pop up. Michael Cohen Scott Lawrence wrote:Great. Just make sure it doesn't come with a performance hit. On 12/29/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote:So I *think* we might be able to make a cross-platform sandbox. Well, make is not quite the write word. "Use". Google's Native Client is designed to make safe, cross-platform native code for use as a browser plugin, but apparently the sandboxy part is available separately. If we can get this working, this would let the client send the *same native code* to the Windows and Linux clients, and have them *both* execute it safely (since it uses system-call-free code). I am checking out the source now. Michael Cohen Scott Lawrence wrote:Short answer: no. Long answer: We're not writing a C sandbox that works on windows/non-unix. That's the only restriction. Windows people can run the java, perl, python, and whatever other clients we write. Furthermore, they can submit code with a C client, but there better be a java client to run code to give them CPU time credits (provided that the cluster they're using has that feature enabled). On 12/28/09, Frederic Koehler <fkfire@xxxxxxxxx> wrote:Um...Are we going to require that all clients run linux? On Mon, Dec 28, 2009 at 11:08 PM, Michael Cohen <gnurdux@xxxxxxxxx> wrote:ptrace tells you whenever the process tried to make a system call. You can then do whatever you want with that information, including recording it and passing it on to the kernel or doing your own action. Michael Cohen Scott Lawrence wrote:Actually, not. Ignore that last message. Can you build a prototype, that calls a specified function in place of the kernel?? On 12/28/09, Scott Lawrence <bytbox@xxxxxxxxx> wrote:Ok. I think that for the most part, we should block system calls. On 12/28/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote:Very little to not at all if the code doesn't make many system calls. I wouldn't expect it to make many anyway; the tasks that this is good for shouldn't be ones that require much communication (because the Internet is fairly slow; if it's always sending stuff and requiring responses that gives probably a .1 second latency each step at least), so its mostly just running on the CPU. It would certainly add less overhead for CPU-intensive things than say, Java. Michael Cohen Scott Lawrence wrote:And this is the only thing that needs to be done? How much will it slow the code down? More importantly On 12/28/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote:We can't actually block interrupts; that require kernel mode code. Also, I think there are other mechanisms for system calls. BUT lucky for us, Linux (and other unixes, but with slightly different implementations) has a built-in way to intercept system calls. It's called ptrace, and it is what is used for the USACO sandbox. Michael Cohen Scott Lawrence wrote:Oh. I see. My first instinct is to say: "ban them!" But it would be really nice if most existing source code could run out-of-the-box on the cluster, even if there wouldn't be a speedup. I'm not planning on support C/C++ on windows - that's way too much trouble - so we only have to worry about unix systems. Are interrupts the only things we would have to block? On 12/28/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote:You are simply incorrect here. The issue isn't library calls, it's system calls. Libc calls themselves use system calls, which are interrupts. You can do everything without touching libc. You just do the right stuff to the stuck and do an interrupt or whatever. The library doesn't have some special way to access the kernel. Michael Cohen Scott Lawrence wrote:You're all missing the point. I'm claiming that, properly implemented, Modred should require no sandboxing outside of what is necessary to implement it's logic. So back to our good friends Alice, Bob, and Mallory. Alice sends the cluster (which means she directs it to the hub, but let's just consider the cluster a big black box for now) some C source code. This code does some strange stuff - lots of file i/o and memory access. What does the cluster do with this? It links the program with its own special libraries. Even inline assembly has to call functions to interface with the hard drive and allocate memory and such. Malicious code that gets submitted to the server will be sanitized in this fashion. The only problem I see is with illegal memory access - but I suspect this will be dealt with, because the cluster has to analyze what data the client program accesses anyway... Now Bob wants to compile and link his program on his own computer. Fine. He uses a different (smaller, incidentally) set of libraries. These libraries don't intercept every call of malloc and stuff - those are run on his computer. But if he wants to access cluster data, he has to use special functions. And he can't actually run code on the cluster. Now what does Mallory do again? On 12/28/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote:Server-side I don't see an issue. (java's, lua's, > javascript's, .NET/mono, some other random thing) is basically what I already said. There are other sandboxing systems that are designed to work on x86 native code, such as vx32 (I think I mentioned that also). Many of these schemes (with the exception of vx32) have the advantage that they also automatically make the code cross-platform. Even vx32 is supposedly portable to Windows, but nobody has done it yet and I have no idea if any of us have the expertise to. Frederic Koehler wrote:As far as sandboxing, server-side you can presumably rely on the operating system's sandboxes (per-user or perhaps some more elaborate mechanism like FreeBSD's jails). But as soon as the cluster sends code out to clients, obviously there is a big issue if we let them do whatever the hell they want. Just preventing assembly or anything like that simply doesn't work in C/C++, (not to mention it would be suprisingly hard/irritating,) since the code could still execute the system-calls (you could try not linking against libc,too, but then you _really_ have no portability :P). System-call controlling is possible, but is either pretty unportable (lots of x86 assembly stuff) or slow-ish (virtual machines). That being said, if you completely seperate client-sendable code from server-code, I think that allays a lot of the concerns. Requiring client-sendable code to be written for some safe VM (java's, lua's, javascript's, .NET/mono, some other random thing) could avoid this. In addition, client-sendable code would intentionally be written with knowledge of the sensitivity of the data it handles (i.e. not written at all if the data is important). On Mon, Dec 28, 2009 at 7:49 PM, Michael Cohen < gnurdux@xxxxxxxxx> wrote: I would still be happier if there were a sandbox, actually.There are ways of getting around that sort of thing that are too complicated to prevent at the source level IMO. For instance, you can use inline assembly. So we block inline assembly. That's all well and good, but now we've blocked people using legitimate assembly optimizations. Worse, what happens if they execute some shellcody stuff, allowing them to escape? I don't really know how to block that at all. On the other hand, a sandbox would not add much overhead since these tasks will most likely use lots of CPU time but few system calls or whatever. Michael Cohen Scott Lawrence wrote: Ok, I'm going to build a prototype of my privacy model. I'mnot going to implement the challenge-response stuff, I'll assume there's an implementation of that and that it works. I think I've isolated the misunderstanding about the sandboxes. You don't submit binary code the the Modred cluster - you either submit source, to be linked by the modred cluster with the relevant libraries, or you link the code yourself with the libraries. The libraries that you would link with merely copy the program over to the cluster, where it can be executed in a manner deemed fit by the code there. I suppose you could say that that is a sandbox. ;-) On 12/28/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote: If you read my email more carefully, you will see that I amnot necessary objecting to Scott's suggestion. I say that it is not necessary, but that it would be the only thing necessary to allow more problem-specific privacy tasks to be used. The need for a sandbox is pretty simple. If we make untrusted users able to ask for tasks, if they upload code, then I don't want it running unsandboxed on my computer. Otherwise, their code could steal my files, wipe my harddisk, install Windows or do other undesirable things. If it is sandboxed, then arbitary code can be executed safely, as long as we trust the sandbox. Sandboxed environments are often also cross-platform, another plus, since they typically replace or intercept any kind of system call. Michael Cohen Scott Lawrence wrote: Well, I'm glad someone expresses opinions I don't agreewith... I think Mikey's objection to privacy concerns is that it's so problem-specific, we can't reasonably expect to have a general implementation. But if the user specifies which parts of the data are private, the Modred hub just has to be sure to divvy up tasks in a way that gives those bits of information only to the trusted, dedicated servers. For the purposes of clarity, I will be referring to dedicated servers as simply "servers", and the central server as the "hub". I don't see the need for a sandbox. Could you present some specific attacks that a sandbox would fix? On 12/28/09, Michael Cohen <gnurdux@xxxxxxxxx> wrote: It seems to me that dealing with privacy concerns is anextremely problem-specific issue. In any given case you need to work out how much you can give to people without letting private information leak, but the details vary greatly from problem to problem. That isn't our business, and I don't think we should concern ourselves with it too much. The way I see it there are two options: 1. make this designed for stuff without privacy concerns I think this is both the easiest and the best option. I don't really like the idea of a public, free service doing computations for an evil corporation anyway; if it's being done BY the public it should be done FOR the public. 2. add in a small amount of functionality designed to facilitate dealing with privacy concerns At the level of this project, that would probably just be the controls on what data gets sent to what people. There might be reasons for adding such controls anyway; some tasks could be designated for only "trusted" users. Either way I doubt that this will be a big issue. I think maybe a bigger issue is how to run arbitrary code efficiently and securely. I see only a few solutions Don't allow arbitrary code, but only a defined set of tasks. Or, similarly, allow some "trusted" set of tasks, each separately ported to each platform (like boinc). Use Java. This lets us easily sandbox it and is cross-platform, but sacrifices a bit on efficiency. Also, Java can be annoying (although other JVM languages would also work in this situation). There are ways of running cross-platform, C/C++ code in a sandbox as well. One possibility is to use LLVM, although the LLVM developers specifically say that LLVM is NOT designed to be used this way. Another possibility is to use a sandboxed code system that works on multiple operating systems but only on x86. This includes things like VX32, which is apparently portable to Windows, but hasn't been ported. I don't know whether or not that sort of thing is within our abilities. Another option might be Google Native Client; that is designed to be used in a web browser but I don't know how hard it would be to "rip out" the sandboxing/cross-OS x86 code stuff. Michael Cohen _______________________________________________ Mailing list: https://launchpad.net/~modred Post to : modred@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~modred More help : https://help.launchpad.net/ListHelp _______________________________________________Mailing list: https://launchpad.net/~modred Post to : modred@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~modred More help : https://help.launchpad.net/ListHelp _______________________________________________Mailing list: https://launchpad.net/~modred Post to : modred@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~modred More help : https://help.launchpad.net/ListHelp _______________________________________________Mailing list: https://launchpad.net/~modred Post to : modred@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~modred More help : https://help.launchpad.net/ListHelp _______________________________________________Mailing list: https://launchpad.net/~modred Post to : modred@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~modred More help : https://help.launchpad.net/ListHelp _______________________________________________Mailing list: https://launchpad.net/~modred Post to : modred@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~modred More help : https://help.launchpad.net/ListHelp_______________________________________________ Mailing list: https://launchpad.net/~modred Post to : modred@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~modred More help : https://help.launchpad.net/ListHelp-- Scott Lawrence Webmaster The Blair Robot Project Montgomery Blair High School_______________________________________________ Mailing list: https://launchpad.net/~modred Post to : modred@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~modred More help : https://help.launchpad.net/ListHelp_______________________________________________ Mailing list: https://launchpad.net/~modred Post to : modred@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~modred More help : https://help.launchpad.net/ListHelp_______________________________________________ Mailing list: https://launchpad.net/~modred Post to : modred@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~modred More help : https://help.launchpad.net/ListHelp
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