Messages in this thread | | | Subject | Re: Out of tree module using LSM | From | Jon Masters <> | Date | Thu, 29 Nov 2007 14:45:51 -0500 |
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On Thu, 2007-11-29 at 11:11 -0800, Ray Lee wrote: > On Nov 29, 2007 10:56 AM, Jon Masters <jonathan@jonmasters.org> wrote: > > On Thu, 2007-11-29 at 10:40 -0800, Ray Lee wrote: > > > On Nov 29, 2007 9:36 AM, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote: > > > > > closed. But more importantly further access to it can be blocked until > > > > > appropriate actions are taken which also applies with your example, no? Is > > > > > > > > That bit is hard- very hard. > > > > > > In some sense it seems like the same problem faced by dynamic > > > translators such as Qemu. They really want to vet a dirtied or faulted > > > page before allowing the app to run unhindered. It's be nice to have > > > some way to do that without virtualizing the whole of userspace. > > > > Like I hinted at, you can't just "vet a page". Because a page alone is > > meaningless garbage, unless it happens to be an extremely small program, > > with headers, all nicely aligned. Most likely you don't know if a random > > page of data is code from a COFF file, ELF file, or some random crap I > > typed in at a terminal after having too much coffee. > > > > So. You'd need to scan *all the pages* of *the entire file*, every time > > that you performed any type of operation. > > *blink* Really?
Yeah, really.
> To lift Alan's example, a naive first implementation > would be to create a suffix tree of all of ESR's works, then scan each > page on fault to see if there are any partial matches in the tree.
Ah, but I could write a sequence of pages that on their own looked garbage, but in reality, when executed would print out a copy of the Jargon File in all its glory. And if you still think you could look for patterns, how about executable code that self-modifies in random ways but when executed as a whole actually has the functionality of fetchmail embedded within it? How would you guard against that?
Jon.
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