Messages in this thread | | | Date | Mon, 22 May 2006 10:33:52 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH] 2.6.16.16 Parameter-controlled mmap/stack randomization |
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Hi!
> >>> On Fri, 2006-05-19 at 21:00 -0400, John Richard Moser wrote: > >>>> Any comments on this one? > >>>> > >>>> I'm trying to control the stack and heap randomization via command-line > >>>> parameters. > >>> why? this doesn't really sound like something that needs to be tunable > >>> to that extend; either it's on or it's off (which is tunable already), > >>> the exact amount should just be the right value. While I often disagree > >>> with the gnome desktop guys, they have some point when they say that > >>> if you can get it right you shouldn't provide a knob. > >> This is a "One Size Fits All" argument. > >> > >> Oracle breaks with 256M stack/mmap() randomization, so does Linus' mail > >> client. That's why we have 8M stack and 1M mmap(). > >> > >> On the other hand, some things[1][2][3] may give us the undesirable > >> situation where-- even on an x86-64 with real NX-bit love-- there's an > >> executable stack. The stack randomization in this case can likely be > >> weakened by, say, 8 bits by padding your shellcode with 1-byte NOPs > >> (there's a zillion of these, like inc %eax) up to 4096 bytes. This > >> leaves 1 success case for every 2047 fail cases. > > > > Maybe we can add more bits of randomness when there's enough address > > space -- like in x86-64 case? > > Yes but how many? I set the max in my working copy (by the way, I > patched it into Ubuntu Dapper kernel, built, tested, it works) at 1/12 > of TASK_SIZE; on x86-64, that's 128TiB / 12 -> 10.667TiB -> long_log2() > - -> 43 bits -> 8TiB of VMA, which becomes 31 bits mmap() and 39 bits stack. > > That's feasible, it's nice, it's fregging huge. Can we justify it? ... > well we can't justify NOT doing it without the ad hominem "We Don't Need > That Because It's Not Necessary", but that's not the hard part around here.
Well, making it configurable and pushing hard decision to the user is not right approach, either. I believe we need different per-architecture defaults, not "make user configure it". Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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