Date: Mon, 29 Jan 2018 22:05:22 +0100 From: Solar Designer <solar@...nwall.com> To: announce@...ts.openwall.com, lkrg-users@...ts.openwall.com Subject: Linux Kernel Runtime Guard Hi, This is to announce our most controversial project ever. Linux Kernel Runtime Guard (LKRG) is a loadable kernel module that performs runtime integrity checking of the Linux kernel and detection of security vulnerability exploits against the kernel. As controversial as this concept is, LKRG attempts to post-detect and hopefully promptly respond to unauthorized modifications to the running Linux kernel (integrity checking) or to credentials (such as user IDs) of the running processes (exploit detection). For process credentials, LKRG attempts to detect the exploit and take action before the kernel would grant the process access (such as open a file) based on the unauthorized credentials. You can download the current experimental version of LKRG at its brand new homepage: http://www.openwall.com/lkrg/ LKRG is mostly due to work by Adam 'pi3' Zabrocki, has been in (re-)development for a couple of years, and builds upon Adam's prior experience with a related project in 2011. I contributed some ideas to the project starting last year, significantly changing the focus of this initial public release. I did not contribute any code yet, though. We would also like to acknowledge related ideas by Kirill Korotaev from CloudLinux / Virtuozzo, who communicated them to me privately a few years ago. And we'd like to mention, as independent related work, the Additional Kernel Observer (AKO) project by Yuichi Nakamura from Hitachi and Toshihiro Yamauchi from Okayama University as announced at Linux Security Summit 2017 and discussed/criticized in: http://www.openwall.com/lists/kernel-hardening/2017/09/22/3 LKRG differs from AKO in a number of ways, including LKRG being an LKM rather than a patch, LKRG performing occasional integrity checking of most of the rest of the kernel and not only of process credentials, and LKRG being less immature. While LKRG defeats many pre-existing exploits of Linux kernel vulnerabilities, and will likely defeat many future exploits (including of yet unknown vulnerabilities) that do not specifically attempt to bypass LKRG, it is bypassable by design (albeit sometimes at the expense of more complicated and/or less reliable exploits). Thus, it can be said that LKRG provides security through diversity, much like running an uncommon OS kernel would, yet without the usability drawbacks of actually running an uncommon OS. As free LKRG becomes somewhat popular and maybe a target of some exploits, we might introduce paid LKRG Pro as a means to fund the project and provide further diversity (with Pro's smaller userbase being beneficial), extra and specialized functionality (e.g., detection of container escapes), and maybe distro-specific binary builds. Like any software, LKRG may contain bugs and some of those might even be new security vulnerabilities. You need to weigh the benefits vs. risks of using LKRG. Our assessment is that the benefit vs. risk ratio for LKRG when used on typical Linux systems isn't nearly as bad as it is for typical Windows anti-virus and end-point security products (which we also find controversial for similar reasons). LKRG's code size and attack surface are much smaller than those products'. If you would use those then you'd probably be OK using LKRG as well. If you wouldn't, or if your Linux systems are otherwise hardened and/or always promptly updated, then you could want to think twice about using LKRG as well. LKRG is most useful for systems that realistically, despite of this being a best practice for security, won't be promptly rebooted into new kernels (nor live-patched) whenever a new kernel vulnerability is discovered. Being a kernel module (not a kernel patch), LKRG can be built for and loaded on top of a wide range of mainline and distros' kernels, without needing to patch those. We currently support kernel versions ranging from RHEL7 (and some of its clones/revisions, including even the heavily modified OpenVZ 7 / Virtuozzo 7, albeit not trying to detect container escapes yet) and Ubuntu 16.04 to latest mainline. LKRG is currently in an early experimental stage. We expect occasional false positives (integrity violations and/or exploits detected when there aren't ones). LKRG's current response to kernel integrity violations is merely reporting those in kernel messages (which obviously doesn't mitigate attacks when those are for real) and its current response to unauthorized process credentials is killing the process (which does defeat many exploits, but is a rather mild response nevertheless). This will likely change as LKRG becomes more mature. To illustrate LKRG's exploit detection capabilities, in our testing on vulnerable distro kernels LKRG successfully detected certain pre-existing exploits of CVE-2014-9322 (BadIRET), CVE-2017-5123 (waitid(2) missing access_ok), CVE-2017-6074 (use-after-free in DCCP protocol). However, it wouldn't be expected to detect exploits of CVE-2016-5195 (Dirty COW) since those directly target the userspace even if via the kernel. While in case of Dirty COW the LKRG "bypass" happened due to the nature of the bug and this being the way to exploit it, it's also a way for future exploits to bypass LKRG by similarly directly targeting userspace. It remains to be seen whether such exploits become common (unlikely unless LKRG or similar become popular?) and what (negative?) effect on their reliability this will have (for kernel vulnerabilities where directly targeting the userspace isn't essential and possibly not straightforward). We did not focus on performance optimizations nor ran many benchmarks yet, but to give a rough idea the performance impact of LKRG 0.0 on building John the Ripper 1.8.0 with "make -j8" on an Atom C2750 machine (8 Silvermont cores in 20W TDP) running VzLinux (Virtuozzo 7) appears to be around 6.5%. We find this performance impact significant (especially for a security measure bypassable by design), and are likely to make adjustments to reduce it. More information on LKRG is available on our wiki, you're welcome to support the project on Patreon, and we've also setup a mailing list for discussions around LKRG - lkrg-users. The corresponding links are available on the LKRG homepage referenced above. Please direct any questions or comments on LKRG to the lkrg-users mailing list. Thanks for scrolling down this far. Alexander
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