Big problems with ASLR in Ice Cream Sandwich

http://blog.duosecurity.com/2012/02/a-look-at-aslr-in-android-ice-cream-sandwich-4-0/

by trhaynes • 14 years ago

63 18 14 years ago

blog.duosecurity.com

tytso2• 14 years ago

The problems which were pointed out are good ones, and they should be fixed. Fortunately, they are easy to fix.

In the grand scheme of things, though, this isn't as bad as it seems, since the vast majority of Android applications run in the Dalvik JVM. Hence the amount of code that is subject to weaknesses that could be exploited by the attacker to cause a jump into the non-randomized dynamic loader (for example) are much smaller.

Of course, there could still be bugs in native code applications, libraries, and system executables, so the ALSR should definitely be improved. Again, fortunately, this should be relatively easy to do.

jonoberheide5• 14 years ago

There's still a large attack surface of native code in the Android platform. I've heard WebKit has a few bugs... :-P

ch0wn• 14 years ago

This is why I think Chrome for Android is a big deal. The browser will always be one of the easiest ways run an exploit. With the browser tightly coupled with the OS, many old phones will never receive an update for it.

The WebView as attack target is a different story, though.

alecco• 14 years ago

You made a great point. Why did you have to ruin it with an emoticon?

saurik3• 14 years ago

Yes, it should be easy to fix. That said, you downplay the weakness too strongly: it was because of the lack of working ASLR that allowed me to use the mempodipper exploit (as my port, "mempodroid" [1]) to get root on all the current ICS devices. (While sometimes you can adjust an exploit to work around ASLR, this exploit requires you to know an absolute address before the program executes.)

[1] https://github.com/saurik/mempodroid

jonoberheide5• 14 years ago

Yeah, mempodroid is a great example. You'd need to randomize the location of the setuid executable (w/PIE), randomize of the linker, and implement something like GRKERNSEC_BRUTE to prevent trivial local bruteforcing of a usable address.

Speaking of which, spender's recent blog post gives a good overview of some of the grsec/PaX mitigations that would hamper the exploitation of the /proc/pid/mem vuln:

http://forums.grsecurity.net/viewtopic.php?f=7&t=2939

tytso2• 14 years ago

/me not my current employer speaking

OTOH, that means it's a back door for use with those nasty handset manufacturers that still ship phones that can't be unlocked. :-)

malkia• 14 years ago

So how does the ASLR work with images optimized to be loaded at specific address? (-fPIC all of them?)

I was under the impression that if you have two or more instances of the same .so/.dll/.dylibs in different processes, and they end up using different virtual addresses then they can't share the same code page. Maybe I'm behind times...

jonoberheide5• 14 years ago

Right, all libaries need to be compiled with -fPIC in order to be randomized. That tends to be much more common than -fPIE.

aortega2• 14 years ago

I disagree with -fPIE making things slow, specially in the ~13 general purpose registers of ARM. Maybe -fPIE affect things in the register-starved x86, not so much in modern archs. Also, "fucked up beyond all repair" is a little exagerated when the repair is to add "-fPIE" to some binaries.

eyemac• 14 years ago

> I was under the impression that if you have two or more instances of the same .so/.dll/.dylibs in different processes, and they end up using different virtual addresses then they can't share the same code page. Maybe I'm behind times...

By design, dylibs (i.e. shared dynamic libraries) are allowed to be loaded at different virtual addresses and still have their text/ro sections shared.

Because dylibs are always compiled with -fPIC, they do not have any dependence on their load addresses (branches are pc-relative, data loads go through the GOT, etc). This allows the dyld to map the physical address(es) of a dylib's text/ro section(s) into virtual address spaces of multiple processes with very little relocation.

Big problems with ASLR in Ice Cream Sandwich

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