Hi Hanno, On Thu, Dec 11, 2014 at 10:45:01PM +0100, Hanno Böck wrote: > Hello, > > I already reported this into your bugzilla, however Greg KH told me it > might be a better idea to post it here: > > With current Linux kernels it seems the address randomization for > loading the vdso library is not that random and can easily be > bruteforced. > > This can easily be demonstrated. Get libvdso address from one > executable: > $ ldd /usr/bin/less|grep vdso > linux-vdso.so.1 (0x00007fff73bfe000) > > Now run ldd mutliple times and check if the same address appears: > c=0; while (true); do let c=c+1; ldd /usr/bin/less|grep > 0x00007fff73bfe000; [ "$?" == 0 ] && echo $c; done > > It usually takes only a few seconds and around 1000-2000 tries until > the loading address is repeated (note that results may vary, it seems > the randomization is biased, some values repeat more often than others). > > This information is mostly from this blog entry: > http://v0ids3curity.blogspot.in/2014/12/return-to-vdso-using-elf-auxiliary.html > And here's a thread on oss-security discussing the issue: > http://www.openwall.com/lists/oss-security/2014/12/09/10 > > The latest version of paxtest added a check for this that guesses the > randomness of vdso: > https://grsecurity.net/~spender/paxtest-0.9.13.tar.gz $ ./randvdso > VDSO randomisation test : 11 quality bits (guessed) > > Bugzilla entry: > https://bugzilla.kernel.org/show_bug.cgi?id=89591
I'm hoping this will get addressed as part of the discussion around the "ASLRv3" patches. PIE (as well as VDSO) randomization has been a per-arch implementation, and it would be best to unify this in a common high-entropy solution. I think the problem with VDSO right now is that it is randomized in relationship to the stack, rather than being randomized on its own. -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
