The Case For Grsecurity

The Case For Grsecurity

The Case For Brad Spengler Open Source Security, Inc. 2012 Overview What is grsecurity? History Why grsecurity exists Recent advances Response strategy Future improvements What is grsecurity? Kernel patch for Linux 2.6.32, 3.2, and

the current stable Linux Provides access control, auditing, chroot hardening, anti-bruteforcing, antiinfoleaking Includes PaX for defense against exploitation of memory corruption vulns (and more) What is grsecurity? (cont.) Goals of detection, prevention, containment Drive up exploit development costs, hopefully require specific targeting Psychology of uncertainty attempt using 0day and risk losing not only the vuln but exploit vectors used? What is grsecurity? (cont.)

Ideal for webhosting environments First work was in webhosting, so I experienced the problems first-hand Very difficult security environment, cant just throw Apache in a VM Generally years ahead of mainstream security

See f=7&t=2574for some examples History Feb 18, 2000 - First release then called GRKERNSEC Poor

port of Openwall to 2.4 kernels 2.4 unsupported by Openwall at the time 2001 Included PaX 2001 Michael Dalton creates Oblivion ACL system for grsecurity History (cont.) Aug 3, 2002 I create learning mode for ACL system Sept 2002 Anti-bruteforcing, IP tagging/tainting April 6, 2003 RBAC system, more advanced learning (full system policies)

2004 - HIDESYM 2009 USERCOPY, limited size overflow prevention, MODHARDEN, fptr constifying See Why grsecurity Exists Because a few hours over a couple months nets: Why grsecurity Exists (cont.) I'll be curious to see what the CVE statistics are like for the kernel this year when they get

compiled next year -- I'm predicting that when someone's watching the sleepy watchers, a more personal interest is taken in doing the job that you're paid to do correctly. exp_moosecox.c, 2009 Why grsecurity Exists (cont.) Culture

of anti-security upstream I literally draw the line at anything that is simply greppable for. If it's not a very public security issue already, I don't want a simple "git log + grep" to help find it. Linus Torvalds, LKML I just committed this to mainline, and it should also go into stable. It's a real DoS fix, for a trivial oops (see the security list for example oopser program by Oleg), even if I didn't want to say that in the commit message ;) Linus Torvalds, not LKML I have tried to camouflage the security fix a bit by calling it a PROT_NONE fix and using pte_read(), not pte_user() (these are the same on x86). Albeit there's no formal embargo on it, please consider it embargoed until the fix gets out. Ingo Molnar, 2005, private bugtraq for RHEL Why grsecurity Exists (cont.)

Vendor-sec compromised at least twice 2005, 2011 (finally shut down) No accountability, sat on IA64 hardware DoS for two years Embargoed vulns basically guaranteed head-start for blackhats Replacement list is better, but lessons learned from vendor-sec show failure of reactive security Users disempowered when information is controlled by a few (see

e-process-poll-results/, decision to pre-release to genuine cloud providers) Why grsecurity Exists (cont.) Eight stable kernel trees Upstream focus is on adding new features (with new vulns) From series of infoleak vulns found by Mathias Krause (minipli): 11 affected 2.6.32 (released 2010) 15 affected 3.2 (released Jan 2012)

17 affected 3.5 (released July 2012) Why grsecurity Exists (cont.) Vuln is DoS if not clever enough to exploit See sudden spike in 2009 of privesc Generally beyond copying grsecurity, that is Find

no defense in depth on the kernel level bug / patch bug cycle Whitelist vs blacklist Exploit vectors vs vulnerabilities The many eyes of open source are blind, uninterested, or selling to governments for profit (its not the 1992 AD scene anymore) Why grsecurity Exists (cont.) 3.x uname stack infoleak fixed in grsec Sept

19th, mentioned in both grsec and PaX changelogs Fix 3.x uname emulation infoleak in grsec fixed kernel stack disclosure in sys_newuname affecting linux 3.x in PaX Not spotted for several weeks by anyone else, notified Google Patch submitted recently, finally in Linus tree Oct 19 Many

eyes, right? Recent advances Since 2011: GRKERNSEC_BRUTE Bruteforce deterrence for suid/sgid binaries GRKERNSEC_MODHARDEN mount via root can only auto-load

filesystem modules Netdev code can only auto-load netdev modules No udisks auto-load Recent advances (cont.) Since 2011: GRKERNSEC_KERN_LOCKOUT Attack by uid 0 or in interrupt handler, panic() Attack by non-priv user, ban until reboot

PAX_USERCOPY Whitelisting of slab caches that can be used for copies to/from userland Ex: no copying to/from cred, task, dentry structs Recent advances (cont.) Since 2012: GRKERNSEC_PTRACE_READEXEC Disallow

ptracing unreadable binaries GRKERNSEC_SETXID Uid 0 setuid to non-root, change performed across all threads Required per-arch changes GRKERNSEC_SYMLINKOWN Race-free implementation of Apaches SymLinksIfOwnerMatch Recent advances (cont.) Since

2012: GRKERNSEC_PROC_MEMMAP Per-CPU, non-overflowable exec ID to ensure sensitive /proc entries can only be read/written by the same process that opened them Arg/env pages limited to 512KB for suid/sgid binaries (defuse entropy reduction) RLIMIT_STACK bounded, 3GB personality cleared to prevent alternate memory layout for suid/sgid binaries Recent advances (cont.)

Since 2012: GRKERNSEC_HIDESYM Reused PAX_USERCOPY slab cache whitelisting code, made generic caches Made seqfile code allocate out of whitelisted generic cache Added check to *printf() that sanitizes kernel pointers printed with %p in buffers allowed to be copied to userland Prevented useful leak via /proc/net/ptype (hi Dan!) Recent advances (cont.) Backported ~110 security fixes to the kernel in 2012 that upstream missed Notified maintainer, who added ~70 of these to based on my changelogs Number of backports are even higher for newer kernels, as many vulns are in code recently introduced Response strategy Motivation for many advances: spite Scorched-earth exploit response

A scorched earth policy is a military strategy or operational method which involves destroying anything that might be useful to the enemy while advancing through or withdrawing from an area. Wikipedia Upstream kills the vulnerability exploited, we kill exploit vectors found along the way Must be weighed against produced disincentive to publish, as this harms reactive security users more than us Response strategy (cont.) Stackjacking (2011)

30 minutes advance notice, killed in a week before repeat presentation Original presentation demo needed an artificial, best-case arbitrary-write and infoleak vuln 6 enhancements made to grsecurity/PaX which have been improved further since A year later, still presenting on the same techniques that were promptly demolished by the PaX Team Jon Oberheide

Response strategy (cont.) Sudo format string vuln (VNSecurity, 2012) 6 improvements made to grsecurity/PaX Most already mentioned Increased heap randomization in higher order bits Increased stack randomization in lower order bits on x64 Small randomization in gap between program stack and arg/ env strings Despite all this, however, VNSecurity still able to create a one-shot exploit, aided by some unique sudo characteristics

Very nice work! See the progression here: Short term vs long term strategy Future improvements Kernel self-protection in place pushes many exploits into the code-reuse + infoleak space Drive up complexity of code reuse, force some data attacks into this space (e.g., cred struct modification) Eliminate known offsets/heuristic scanning as a technique against important kernel targets (GCC plugin)

Future improvements (cont.) Make it easier official, unique kernel packages without distro kernel drawbacks RBAC improvements Improved learning system using real machine learning algorithms instead of heuristics Not just reduction of path accesses to directories, but regular expression learning for more usable policies across software updates Automatically mark PaX flags for problem apps with a simple configurable daemon

Questions/Requests? Feel free to email me at [email protected] Thanks Most to my sponsors for their support of all, thanks to pipacs and Emese

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