Linux kernel-rootkit-dev - Wonokaerun
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This document contains the slides from a presentation given by WonoKaerun at the Indonesian Security Conference 2011 in Palembang. The presentation introduces rootkits and techniques for hiding malware at the kernel level on Linux systems. It covers topics like loadable kernel modules, interrupt descriptor table hooking, virtual file system hacking, page fault handler hijacking, debugging register abuse, and kernel instrumentation patching. The goal is to evade detection by security solutions by gaining control of the kernel before anti-rootkit defenses can activate. Throughout, the document emphasizes the cat-and-mouse nature of offensive and defensive security research.
![ Historically, LKM-based rootkits used the
„sys_call_table[]‟ symbol to perform hooks on the
system calls
sys_call_table[__NR_sc] = (void *) hacked_sc_ptr;
However, since sys_call_table[] is not an exported
symbol anymore, this code isn‟t valid
We need another way to find „sys_call_table`[]](https://image.slidesharecdn.com/linux-kernel-rootkit-dev-110725024131-phpapp01/85/Linux-kernel-rootkit-dev-Wonokaerun-10-320.jpg)
![1.b. Finding SysCallTable Address
1. Get the IDTR using SIDT
2. Extract the IDT address from the IDTR
3. Get the address of „system_call‟ from the
0x80th entry of the IDT
4. Search „system_call‟ for our code fingerprint
5. Finally, we should have the address of
„sys_call_table[]‟ !](https://image.slidesharecdn.com/linux-kernel-rootkit-dev-110725024131-phpapp01/85/Linux-kernel-rootkit-dev-Wonokaerun-11-320.jpg)
![1.c. Bypass WP (Write Protection)
- Problem : sys_call_table[] is read-only!
- Solution : We must clear 16th bit of cr0!
static void disable_wp_cr0 (void) {
unsigned long value;
asm volatile("mov %%cr0,%0" : "=r" (value));
if (value & 0x00010000) {
value &= ~0x00010000;
asm volatile("mov %0,%%cr0": : "r" (value));
}
}](https://image.slidesharecdn.com/linux-kernel-rootkit-dev-110725024131-phpapp01/85/Linux-kernel-rootkit-dev-Wonokaerun-12-320.jpg)
![1.d. On x86_64
- Actually this is NOT new architecture, it‟s just
specifically different in memory addresing plus
with additional of new CPU instructions.
- We can find sys_call_table[] by bruteforcing in
range memory address between:
[0xffffffff00000000 – 0xffffffffffffffff]](https://image.slidesharecdn.com/linux-kernel-rootkit-dev-110725024131-phpapp01/85/Linux-kernel-rootkit-dev-Wonokaerun-13-320.jpg)
Linux kernel-rootkit-dev - Wonokaerun
- 1. - WonoKaerun - Indonesian Security Conference 2011 Palcomtech – Palembang 16-17 Juli 2011
- 2. InfoSec Enthusiast Independent IT Security Researcher Slackware & FreeBSD Hobbiest Still.. a Lazy Student #FYM ;) T : @sukebett M : dante at indiefinite.com
- 3. Introduction Definition Classification Main Contents Demo Conclusion
- 4. Rootkit Source: http://www.flickr.com/photos/jraptor/4459405455/
- 5. Ring0 Source: http://www.imdb.com/title/tt0235712/
- 6. Ring0 Source: http://www.acm.uiuc.edu/projects/RingCycle/wiki/ProtectionModel
- 7. Ring0 Levels Rootkit “Rootkits that are running at Kernel Mode!” Source: http://www.rayheffer.com/139/running-rings-around-virtualisation/
- 8. 1. LKM Based Rootkit 2. Non-LKM Based Rootkit - So, What is LKM (Loadable Kernel Module)? Source: http://www.ragepk.com/fn 5.7 Millimeter Pistol.html
- 9. 1.a. Hooking System Call Table Address Source: http://www.slideshare.net/fisher.w.y/rootkit-on-linux-x86-v26
- 10. Historically, LKM-based rootkits used the „sys_call_table[]‟ symbol to perform hooks on the system calls sys_call_table[__NR_sc] = (void *) hacked_sc_ptr; However, since sys_call_table[] is not an exported symbol anymore, this code isn‟t valid We need another way to find „sys_call_table`[]
- 11. 1.b. Finding SysCallTable Address 1. Get the IDTR using SIDT 2. Extract the IDT address from the IDTR 3. Get the address of „system_call‟ from the 0x80th entry of the IDT 4. Search „system_call‟ for our code fingerprint 5. Finally, we should have the address of „sys_call_table[]‟ !
- 12. 1.c. Bypass WP (Write Protection) - Problem : sys_call_table[] is read-only! - Solution : We must clear 16th bit of cr0! static void disable_wp_cr0 (void) { unsigned long value; asm volatile("mov %%cr0,%0" : "=r" (value)); if (value & 0x00010000) { value &= ~0x00010000; asm volatile("mov %0,%%cr0": : "r" (value)); } }
- 13. 1.d. On x86_64 - Actually this is NOT new architecture, it‟s just specifically different in memory addresing plus with additional of new CPU instructions. - We can find sys_call_table[] by bruteforcing in range memory address between: [0xffffffff00000000 – 0xffffffffffffffff]
- 14. 1.e. Capabilities - Hiding File/Directory - Hiding Process - Hiding Network Traffic - Sniffing - Keylogging - Etc..
- 15. 1.f. References - http://thc.org/papers/LKM_HACKING.html - http://www.phrack.org/issues.html?issue=52&id=18 - http://www.slideshare.net/fisher.w.y/rootkit-on- linux-x86-v26 - http://www.exploit-db.com/papers/13146/
- 16. 2.a. IDT(Interrupt Descriptor Table) Handling - Interrupt: “An event that alters the sequence of instructions executed by a processor. Such events correspond to electrical signals generated by hardware circuits both inside and outside of the CPU chip.” (Understanding the Linux kernel ,O‟reilly) - The IDT is a linear table of 256 entries which associates an interrupt handler with each interrupt vector, and each entry of the IDT is a descriptor of 8 bytes which blows the entire IDT up to a size of 256 * 8 = 2048 bytes.
- 17. 2.b. Hijacking Methods 1. Create a fake IDT handler 2. Copy our handler's address into new_addr 3. Make the idt variable point on the first IDT descriptor, via idt, idtr dan sidt. (Ref. Phrack 58 article 7) 4. Save the old handler's address (with get_stub_from_idt() function) 5. new_addr contain our handler's address!
- 18. References - http://www.phrack.org/issues.html?issue=59&id=4 - http://codenull.net/articles/kmh_en.html - http://burrowscode.wordpress.com/2010/06/23/idt- hookingunhooking-module/
- 19. 3.a. VFS(Virtual File System) Hacking - VFS and /proc 1. It is a filesystem 2. It lives completely in kernel memory - All access from the userland is limited to the functionality of VFS layer provided by the kernel, namely read, write, open and alike system calls . - So, how the kernel can be backdoored without changing system calls?
- 20. 3.b. System Call Flow in VFS Hijacking Source: http://www.porcupine.org/forensics/forensic-discovery/chapter5.html
- 21. References - http://www.phrack.org/issues.html?issue=58&id=6 - http://www.phrack.org/issues.html?issue=61&id=14 - http://www.trapkit.de/research/rkprofiler/rkplx/rkplx.html
- 22. 4.a Page Fault Handler Hijacking - “A page fault exception is raised when the addressed page is not present in memory, the corresponding page table entry is null or a violation of the paging protection mechanism has occurred.” (Underdstanding The Linux Kernel, O‟reilly) - When? -> The kernel attempts to address a page belonging to the process address space, but either the corresponding page frame does not exist (Demand Paging) or the kernel is trying to write a read-only page.
- 23. 4.b. Schema on Page Fault Hijacking Process Source: http://book.opensourceproject.org.cn/kernel/kernel3rd/opensource/0596005652/understandlk-chp-9-sect-4.html6
- 24. 4.c. References - http://www.phrack.org/issues.html?issue=61&id=7 - http://www.s0ftpj.org/bfi/dev/en/BFi12-dev-08-en - http://whatisthekernel.blogspot.com/2005/09/back- door-entry-getting-hold-of-kernel_01.html
- 25. 5.a. Abusing Debug Register “The IA-32 architecture provides extensive debugging facilities for use in debugging code and monitoring code execution and processor performance. These facilities are valuable for debugging applications software, system software, and multitasking operating systems.” - A debug exception (#DB) is generated when a memory or I/O access is made to one of these breakpoint addresses. - There are 8 debug registers supported by the Intel processors, which control the debug operation of the processor (dr0-dr7).
- 26. 5.b. Debug Register Address Source: http://www.slideshare.net/fisher.w.y/rootkit-on-linux-x86-v26
- 27. 5.c. References - http://www.phrack.org/issues.html?issue=65&id=8 - http://seclists.org/dailydave/2008/q3/224 - http://l33ckma.tuxfamily.org/?p=174 - http://darkangel.antifork.org/publications/Abuso dell'Hardware nell'Attacco al Kernel di Linux.pdf - http://packetstormsecurity.org/files/view/57016/ mood-nt_2.3.tgz
- 28. 6.a. Kernel Instrumentation Patching - Kprobe “Simple method to probe the running kernel. At a fundamental level, it requires the address of a kernel function that needs to be debugged”. - Jprobe “Jprobe is another kind of probing technique, which can be used to access the target function‟s arguments, and thus display what was passed to the function”. - Kretprobes “A return probe fires when a specified function returns ”.
- 29. 6.b. Schema of Kprobe and Jprobe Execution Kprobes Flow Execution Jprobes Flow Execution
- 30. 6.c. References - http://www.phrack.org/issues.html?issue=67&id=6 - http://www.chunghwan.com/systems/gaining- insight-into-the-linux-kernel-with-kprobes/ - http://lxr.osuosl.org/source/Documentation/ kprobes.txt
- 31. Hiding Modules - if(m->init == init_module) list_del(&m->list); - kobject_unregister(&m->mkobj.kobj); //kobject_del for < Kernel 2.6.7
- 32. Non-LKM Rootkits - Via /dev/kmem - Via /dev/mem - How about /dev/port?
- 33. IT’S SHOW TIME! No POC = HOAX!
- 34. “Any rootkit created with existing detection capabilities in mind will evade the protective measures provided by such systems. Warfare at kernel level comes down to a question of who takes over first – the rootkit or the anti-rootkit solution.” (http://www.securelist.com/en/analysis?pubid=204792011)
- 35. “Subtle and insubstantial, the expert leaves no trace; divinely mysterious, he is inaudible. Thus, he is the master of his enemy's fate.” - The Art of War, Sun Tzu