Date: Wed, 10 Dec 2014 13:27:24 -0500 From: Daniel Micay <danielmicay@...il.com> To: Steve Grubb <sgrubb@...hat.com>, oss-security@...ts.openwall.com Subject: Re: Offset2lib: bypassing full ASLR on 64bit Linux On 10/12/14 11:11 AM, Steve Grubb wrote: > On Tuesday, December 09, 2014 03:24:39 PM Daniel Micay wrote: >>> I studied this area 2 years ago for a gray hat talk and in preparation to >>> help set the policy going forward for Fedora and RHEL. The general >>> reason I've heard mentioned about why its not used as fully as possible >>> is that it adds memory pages that can't be coalesced or consolidated >>> because they are not the same. >> >> AFAIK, it doesn't cause a significant increase in memory usage. The >> whole point of position independent code is that it can be reused across >> processes. Dynamic libraries are already fully position independent. > > This was the issue as I remember it, when you use PIE, it introduces a > writable memory segment for the indirection that is filled in lazily. Because > this is writeable it is per process. It is also per DSO. With desktop apps > linking against a 60 or so libraries and an average of 150 apps running at any > time, the memory used starts to really add up. Server workloads tend to have > apps with less libraries linked in but many more processes active. > > Of course today systems are starting to ship with 16GB standard, but now we > add virtualization work loads and you have dozens more of the above. I think > this institutional memory of the old days kind of hinders any movement. We had > an internal debate of this on bz 786915 (which is not 100% open). The start up > performance never really a factor in the discussions. It was purely about > "wasted" memory. The GOT/PLT is still there without PIE. You can blame features like LD_PRELOAD for this, not ASLR. Every library is already paying the costs of PIE and more (-fpie / -fPIE is a subset of -fpic / -fPIC). http://www.macieira.org/blog/2012/01/sorry-state-of-dynamic-libraries-on-linux/ Before the recent GCC / binutils improvements, PIE would result in GOT usage for every global just like PIC. The changes eliminate the need for that so past measurements (which usually indicate a 0-3% perf hit) won't be valid anymore. Download attachment "signature.asc" of type "application/pgp-signature" (820 bytes)
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