Computer Security at the Low, Hardware/Process/Memory Level

1
Computer Security at the Low,
Hardware/Process/Memory Level

• Nicolas T. Courtois -
  University College London

2
Home reading

• Sections 6.3. 6.5.

3

• Where Does Computer Security Come From?

4

• More Precisely
• Some Things You Wanted to Know but Were Afraid To
  Ask

5
Do You Know

• Q1.
• Can in Windows/Linux a process run by an
  administrator access the system/kernel memory?
• Q2.
• Why do we must press CtrlAltDel when we log to
  a PC under many versions of Windows?
• Q3.
• Why more than half of large banks in London
  bought PCs with a pre-installed hardware Rootkit?

6

• PC Software Securitybound to be bad?

7
Bottom Line

• Can we rely on obscurity?
• only for very limited time, few months.
• Software can hardly be protected by software.
• TRUE.
• gt some hardware mechanisms are needed.

8
Remark

• Some industries historically cared MUCH MORE
  about users security than the Wintel guys
• See Applied Cryptography (COMPGA12) module.
• Examples SIM cards, bank cards, building access
  cards, etc

9
Key Remark

• Software CANNOT be protected by software.

10
Bottom Line Not So Bad

• We dont need to have a dedicated certified
  tamper-proof hardware module for everything we
  want to do on a PC
• Good News
• Actually software can be protected by software
  with a little bit of hardware support
• gt this is the objective of todays lecture.

11

• Taxonomy of Threats to Software and OS

12
Taxonomy of Software Threats Microsoft

• Spoofing pretending to be someone else
• Tampering altering data or settings
• Repudiation user denies it was him that did of
  didnt do sth.
• Information disclosure leak of personal
  information
• Denial of service preventing normal operation
• Elevation of privilege e.g. gaining the powers
  of root
• Remark to know this by heart will NOT be on the
  exam, hard to remember, even for me?

13
Impact of Software Threats Microsoft

• Damage potential - lost
• Reproducibility of the threat (hardness)
• Exploitability expertise and resources needed
  for attack
• Affected Users how many users
• Discoverability is attack likely to be detected?

14

• Overview

15
History

• PCs are open source platform based on a set of
  industry-wide standards. gt Only very recently
  there is an evolution towards more closed source,
  and more fragmentation (competing standards)
• 1981. Designed by a team of 12 people.
• Key decisions they took
• Build the machine with "off-the-shelf" parts from
  a variety of different OEMs. Previously IBM had
  developed their own components.
• An open architecture so that other manufacturers
  could produce and sell compatible machines.
• Businesses liked this no lock-in. They bought
  PCs. They knew that they wouldnt be a slave of
  one vendor selling replacement parts.
• The DOS was developed by a small company without
  importance, Microsoft... IBM never made any
  substantial profits

16
Home Reading

• pages 1-12
• short history of Computer Security

17
Standard PC

except it never was multi-user ? ? ? ? ? ?
18
Bottom Line

• Hardware security is better than software.
• Actually software-only security will never exist
  without some hardware that helps it.
• gt in the sense that it provides some
  security functionality.
• Example memory protection.
• A lot of cooperation and support on the OS side
  need to exist as well.
• A security system that Microsoft with Intel
  wouldnt embrace can probably not exist.
• As for Linux systems, they never got into the
  process of industrial innovation. And never
  wanted to secure Hollywood studio movies

19
Least Privilege or Limitation Principle

• Every module (such as a process, a user or a
  program) should be able to access only such
  information and resources that are necessary
  to its legitimate purpose.

20
Main Security Goals For the OSHardware

• (Goal 0.)
• Allowing reliable operation and business
  continuity.
• Goal 1A.
• Allowing multiple users securely share a
  computer.
• Goal 1B.
• Allowing multiple processes securely share a
  computer.
• Goal 2.
• Allow secure operation in a networked environment.

21
Goal 1 Means to Achieve It

• Goal 1AB.
• Allowing multiple users / processes securely
  share a computer.
• memory protection (possibly memory encryption)
• processor modes
• authentication
• file access control and (drive/file) encryption
  and auth.
• logging auditing

22
Goal 2 Means to Achieve It

• Goal 2.
• Allow secure operation in a networked
  environment.
• authentication
• encryption
• resource access control
• intrusion prevention, detection and recovery
• logging auditing

secure channels encrypted and authenticated
23

• Basic Hardware Mechanisms

24

• Memory Protection

25
Memory Protection

• Allows to implement memory access rights for
  processes.
• Goal One process should not access others
  memory.
• Prerequisite Operating system and user processes
  need to have different privileges

26
1) Pre-history of Memory Protection
Problems -multi-user -multi-tasking -flexibility
-sharing
0

• Fence Register
• (OS1 program)
• Base Bound
• (OS several programs)

OS
User
Fence
Runtime checks by CPU

• 2 registers for each program
• -flexibility
• later basebound for each segment but still not
  good enough
• -performance

Program1
Shared
27
Evolution on 1 Slide
-multi-task -multi-user -flexibility -sharing
0

1. Fence Kernel vs. 1 user
2. BaseBound registers for each program
3. Segments rights rwx, each program different
   table
4. Segments Paging
5. Paging only, rwx per page and per program

OS
User
Fence
Program1
Shared
around 200X
Modern PCs
28
Memory Protection History

• In Windows 9x, user processes COULD access system
  memory.
• Though CPUs would allow the separation capacity
  not used!
• Used in
• Most UNIX and Linux systems
• Mac OS X 2001
• Windows NT since NT3.1.
• Windows XP 2001 and ever since.

29
OLD OUTDATED Memory Protection Methods

• Fence Register
• (OS1 program)
• Base Bound
• (OS several programs)
• BaseBound On Per Segment Basis
• (enough flexibility but not efficient and not
  scalable)

30
Fence Register _at_CPU
Addresses
0
Operating System
Problems -Flexibility -Sharing
n
Fence
User Program
n1
high
31
Base Bound Registers
Operating System
User Program A
User Program B
32
Segments

• Split address into two fields
• ltseg, offsetgt
• Each segment has a base bound

1
Fetch lt1,7gt
Operating System
7
User Program A

Seg Base Bnd
0 a b
1 n1 m
User Program B
33
Segments Sharing Protection
different table in each program
Operating System
Seg Base Bnd Prot
0 a n rwx
1 n1 m rw
User Program A

Shared

Seg Base Bnd Prot
0 m1 high rwx
1 n1 m r

User Program B

34
Working With Segments?

• Q1 Are we inside the segment?
• Q2 Do we have the right to write?
• checked at runtime
• costly checks at each memory access
• And how do we manage all this?

35
Memory Management

• Methods further evolved into having
• A hardware memory management unit (MMU) and a lot
  of special circuits in the CPU and chipset.
• A lot of support functions done by the OS.
• A more abstract view where the programmer and the
  compiler would see a simple linear address space.
  Will be achieved with paging

36
Process Memory Layout

0x08048000
Text

• Text loaded from exec code and read-only
  datasize fixed at compilation
• Heap runtime allocated objects, large (2 Gb)
• Stack LIFO, holds function arguments and local
  variables, small size (256 K)

Heap
Grows toward high memory
Grows toward low memory
0x40000000
Stack
0xC0000000
37
Modern Memory Protection Methods

• Segmentation used until recently, no longer used
• Paging the dominant method in 2012
• Capability-based addressing
• the closest to least-privilege ideal.
• But not used in Windows/Linux PCs.

38
Capability Based Addressing

• Not used in commercial PCs
• In Java Virtual Machines
• Also in CapROS (open source, US DARPA-funded
  successor of the defunct Extremely Reliable
  Operating System, supports x86 and ARM)
• How does it work?
• pointers are replaced by special objects called
  capabilities
• only the kernel and special authorized processes
  can create these objects.
• other programs can only use them.

39
Mechanisms Used in Modern PCs

• Segmentation
• Paging
• Work together, though totally independent.
• Each could (only in theory) be disabled.

40
Virtual Memory History

• This architecture exists since i386.
• Later CPUs added more performance and more
  complexity with legacy code compatibility etc

41
Memory Segmentation

• Each memory address is a pair of (segment,
  offset)
• The translation is done by a paged memory
  management unit (MMU).

42
Segmentation Paging Combined

• Before 200X segmentation paging worked
  together, e.g. Intel x32early Windows XP
• However until very recently (even in say 2009)
  there was a big loophole in cheap commercial PCs
  
• no x protection at page level, only at segment
  level

43
Segments - Security

• Each segment had permissions R/W/X.
• If the program uses pointer such that
• it would jump to a segment for which has no X
  right
• it would read memory for which he has no R right
• the offset is outside the allowed range,
• all this is checked by the CPU at runtime
• with help of MMU memory management unit
• a HARDWARE exception 0xEh is raised
• will be handled by OS Kernel

44
Paging

• Virtual Memory, typically 2,3 or 4 Gbytes for a
  32-bit process in Windows.
• Each block is mapped either
• somewhere into memory
• or there is a page fault (OS handles it)
• in the swap (security risk on its own!)
• or not used.
• Some security a page not previously used,
• can automatically generate a page fault error.
• Paging is implemented in hardwaresoftware (part
  of OS).Pages are typically 4K bytes.
• Security each block can be marked as protected.
  (Kernel/OS)

45
Paging

46
Basic Security

• Linux Kernel pages are never swapped to disk.
• Windows similar and more complex.

47
General Protection Fault (GPF)

• It is a hardware mechanism! Exception 0xD.
• Occurs when the program does violate the CPU
  security rules (they are VERY numerous).
  Examples
• using an instruction which can ONLY be used at
  ring 0 by the OS Kernel
• accessing special types of registers and
  Descriptor Tables
• etc
• The OS is expected to catch it and close the
  process
• XP XXX has encountered a problem and needs to
  close. We are sorry for the inconvenience.
• Vista/7 XXX has stopped working.
• If not, if GPF occurs 3 times, (exception within
  exception handler routine) even the OS Kernel
  cannot recover from it.
• gt Must reboot CPU and OS.

48
Segmentation Fault a.k.a. Bus Error

• One example program in C
• char sabcd
• s0//change a to \0
• This will cause segmentation fault, both in
  Unix/Windows because compilers allocate abcd
• in a segment marked as read only.
• Software mechanism, but hardware detection by the
  CPU.
• How does this happen?
• In Linux typically the CPU will notify the OS,
  and the OS will send the SIGBUS signal. Then the
  OS notifies the process which caused the
  exception.
• Under windows goes through exceptions which are
  handled by the code itself

49
Page Protections and Permissions

• Historically, in Intel 32-bit CPUs, permissions
  (R/W/X) exist at segment level, hard to use and
  wasteful.
• Since i386, W/R permissions exist at the page
  table entry level, 4 K pages typically
• implemented in combination of hardware / OS
  kernel with the page descriptors
• ONLY since Pentium 4, X (execution) can also be
  disabled with DEP (later about it)
• BTW No problem ever with i64. R/W/X at page
  level.

50
Vista and Encrypted Paging

• What about memory used for operations on
  protected audio/video content in Vista?
• For example a graphics card using RAM for its
  real-time working data?
• Vista activates a special protection bit
  indicating that they must be encrypted before
  being paged out to the disk, and decrypted back
  again after being paged in.
• But Vista doesnt provide any other page file
  encryption, that programmers could use to protect
  their credit card details or Aes keys or so
• gt Microsoft only cares about Hollywood
  studios.

51
Kernel or Memory Dumps

• If Windows XP crashes
• it will write either a full memory dump, or just
  a Kernel dump into the page file (pagefile.sys).
• temporary.
• after reboot it will be copied to a separate file.

52
ASLR Address Space Layout Randomisation

• Also covered later, see buffer overflow.
  SOFTWARE, not hardware.
• Techniques to randomize at the runtime the layout
  of various pieces of data in memory. Makes it
  much harder for the attacker to predict where the
  data is.
• Example the attacker injects some shellcode in
  a buffer stored on the process stack and
  overwrites some pointers. In his exploit he
  expects consecutive locations. The exploit does
  not work anymore (or with low probability).
• OpenBSD (enabled by default)
• Linux weak form of ASLR by default since kernel
  2.6.12. (much better with the Exec Shield patch
  for Linux).
• Windows Vista and Windows Server 2008
• ASLR enabled by default, although only for those
  executables and dynamic link libraries
  specifically linked to be ASLR-enabled. So only
  very few programs such as Internet Explorer 8
  enable these protections

53
W?X Page Protections in Linux

• What is W ? X?
• Each page should be either writable or
  executable, but not both Exclusive OR
• Applications
• Exe part of the program space (a.k.a. text)
  pages X, not W
• Data pages (stack, heap) mark them as W, not X
• Implementation of W ? X in Linux
• In Linux 32-bit, and with 64-bit CPU, in
  hardware, since Kernel 2.6.8.
• In other cases, mechanism can be implemented in
  software.
• In OpenBSD since version 3.3. May 2003.
• In Linux PaX patch (optional), for 32-bit x86
  processors,
• Tricky way based on segment limit registers and
  segment R/W/X/ permissions
• gt memory x2, really negligible performance
  degradation.

54
Windows DEP Data Execution Prevention

• Old X idea must allow explicitly, current
  OSprograms would stop working.
• The NX idea Never Xecute can forbid. Easier
  to make compatible systems.
• Hardware mechanism. Both Intel and AMD implement
  it but Intel was the last to deliver this benefit
  to large-public CPUs, since P4 Prescott.
• Windows - Since XP SP2.
• Not active by default. Choice dictated by legacy
  programs
• PAE mode needed 64-bit page tables. Bit 63 is
  used.
• Compatibility problems with older processors and
  old motherboards
• Also active in Linux, mostly only on 64-bit CPUs,
  but also with 32-bit Linux,
• in Linux kernel since release 2.6.8 of August
  2004.
• Again can also be enforced purely in software,
  for example in Linux PaX patch (optional Kernel
  patch).

55
Future Curtained Memory

• Not used (as far as I know).
• Expected to work with TP.
• Full isolation of sensitive areas of memoryfor
  example, locations containing cryptographic keys.
  
• Even the OS does not have full access to
  curtained memory.
• Implementation
• Intel's Trusted Execution Technology

56

• CPU Security Features

57
Unique Serial Number

• Routine mechanism in most industries. Unique
  serial number cannot be changed (fixed by the
  manufacturer)
• Example Oyster card, building passes block 0.
• Introduced by Intel since P3.
• can be disabled too, due to privacy advocates
  outcry

58

• CPU Protection Hardware Side

59
Rings Hardware _at_ CPU

• Different CPU architectures define several Rings.
  

60
Transition Calls (Transition Gates)

• Transition only through special system calls
• transfers control to a predefined entry point in
  more privileged code
• the more privileged code does specify and checks
• where it can be entered,
• in which prior processor state one can enter.
• Privileged code, from the processor state and the
  stack left by the less privileged code,
  determines what is requested and allows it or
  not.
• Implementation
• call gates (old) calling directly a Kernel
  function, slow
• INT hardware interruption, saves and restores
  the CPU state, still slow
• Intel and AMD now introduced special faster
  instructions SYSCALL/SYSENTER, SYSRET/SYSEXIT

61
How to Penetrate to Ring 0?

• Whatever you do, it is always possible to get
  there through the boot loader.
• Critical and privileged access point in all PCs.
• Would allow to disable some hardware securities
  such as DEP
• Could allow a virus to be so stealth that no
  anti-virus would detect it.
• Beware of boot sector viruses!
• Good news most motherboards have a hardware
  mechanism that prevents the OS from writing the
  boot sector of the hard drive. No access from the
  O/S level.
• Problem this can be disabled in BIOS.
• which is looking for trouble
• IF this mechanism is totally usable like it
  makes sounds and asks the user to press Y on the
  keyboard, and there is no bug/problem
• THEN it is a bad idea to allow people to disable
  it.

62
How to Still Penetrate to Ring 0?

• More HW mechanisms
• Furthermore, the BIOS has a password (and usually
  also an admin password). But all NVM can be reset
  by a jumper, so it is easy to hack
• Some computer motherboards designed for high
  security customers/applications and certified by
  the government will have better security such as
  
• WORM mechanisms Write Once, Read Many
• unhackable BIOS (more about BIOS sec later)

63
Can We Defend Against Such Threats?

• Yes, or partly so, through logging helped by
  hardware.
• Example 1 a motherboard can have a log of events
  that cannot be erased (WORM).
• Sandisk recently started commercializing WORM
  memory cards (with very large capacity) the
  data can be written but cannot be erased.
• Example 2 Hard disk hardware can make it
  impossible to modify the file creation and
  modification dates of files.
• Then the virus can be detected (removal is
  another story).
• This type of technology is used for forensic
  purposes much more frequently than we think. We
  are just not informed about these extra (hidden)
  features.

64

• CPU Protection (3)
• Hardware OS

65
CPU Modes vs. Modern OS

• DOS the kernel, drivers and applications
  typically run on ring 3, whereas only the 386
  memory manager such as EMM386 run at ring 0
• OS/2 used 3 rings!
• the Multics system had 8 rings
• most current OS and Windows XP use only two rings
  
• ring 0 kernel mode
• ring 3 user mode
• only recently Microsoft have added some ring 1
  code
• there also is a SMM mode, on every PC,
• 16-bit powerful close to ring 0,
• used by the BIOS NOT the OS,
• prevents CPU from overheat etc..
• later about it,

66
CPU Modes Processor Modes Privilege Levels

• Hardware mechanisms that allow the OS to run with
  much more privileges than any process.
• System mode privileged mode master mode
  supervisor mode kernel mode unrestricted
  mode.
• User mode
• Transition only through special system calls or
  privileged instructions or hardware interruptions
  which can only be executed in system mode.
• In theory, only highly-trusted kernel code should
  run in the unrestricted way.
• In practice Real time code such as drivers are
  allowed to also run in the system mode.

67
system mode privileged mode master mode
supervisor mode kernel mode unrestricted mode

• can execute any instruction
• access any memory location
• access hardware devices
• can change a number of special processor
  features
• enable/disable interrupts,
• special registers,
• descriptor tables,
• change privileged/not processor state,
• access memory management units,
• user mode
• access only the usual CPU resources
  computationsregisters
• access to memory is limited,
• cannot access MMUs
• cannot execute certain special instructions,
• cannot disable interrupts, go to privileged
  state, change special registers/tables, etc..

68

• Virtual PCs

69
Virtual PCs VirtualBox, VMWare etc

• recall most current OS
• ring 0 kernel mode
• ring 3 user mode
• using Virtual Box in software mode
• Hosted OS kernel runs at ring 1 replacing 0
• has a real-time code recompiler which replaces
  some instructions
• also does real-time code patching
• cannot run VirtualBox or VMWare inside it because
  cannot create virtual machines
• Hosted OS apps run at ring 3
• but it also can do a hardware assisted mode
• ring 0 is run as ring 0 with isolated memory
• possible only on very recent CPUs

70

• Virtualisation Intel VT AMD-V

71
Intel-VT, a.k.a. Vanderpool

• Main function each virtual Machine running on
  the same CPU has access to all 4 privilege rings.
• Required and used by Windows 7 XP Mode.
• So for example a virtual PCOS cannot detect it
  is a virtual machine by trying CPU instructions
  such as SYSENTER etc.
• Also speeds up running virtual PCs,
• they run much more like a real PC
• better CPU hardware support for paging gt better
  memory isolation
• the difference between real and virtual PCs will
  tend to disappear in the near future
• supported by most but not all current CPUs,
• Intel Atom Z5X0 are OK, Atom 2X0 are NOT OK
• in some motherboards it must be switched on in
  BIOS
• a PC compatible with Intel-VT can run Windows,
  Linux and Mac-OS AT THE SAME TIME as native, no
  need to emulate ring 0 anymore.

72

• BIOS and BOOT security

73
Firmware

• Def a tiny master program included in our PC
• runs first when you switch it on / or reset
• in old times stored in a ROM (Read-Only Memory),
• nowadays most firmware is stored in NOR flash
  devices
• can be updated

74
Traditional BIOS

• BIOS def. a firmware in your PC
• Basic Input/Output System, 25 years old
• Responsible for (picture next slide)
• initialization of much of the system, including
  important components such as video, RAM,
  keyboards and mice.
• POST Power-On Self Test, (NOT hard drives or
  media)
• responsible for finding and loading the OS Boot
• from a number of different types of media,
  ranging from hard disks to USB and LAN devices
  can load option ROMs
• cooperates with the OS load further parts of the
  operating system before the operating system
  completely takes over.

75
Traditional BIOS and Boot source NIST SP800-147

1st device
16-bit insecure mode
can be needed to boot over the network
SMI Handlers Part of BIOSruns in the
background
76
Threats and Attacks

• Firmware update if a virus does it, it can
  circumvent all the OS security Pre-OS attacks
  before the OS loads.
• Malicious updates can enter as
• user-initiated from a bootable disk
• runtime software exploits
• managed BIOS updates inside a company
• new vectors? - self-updating BIOS rootkits?
  Maybe.
• Payload
• Roll-back to old insecure version of BIOS (with
  attacks)
• Install a Firmware Rootkit
• Install a virtualization virus

77
Firmware Rootkits

• Firmware Rootkit def uses device or platform
  firmware to create a persistent malware image in
  hardware, such as a network card hard drive, or
  the system BIOS. The rootkit hides in firmware,
  because firmware is not usually inspected for
  code integrity.
• At BlackHat 2006 Heasman demonstrated the
  viability of firmware rootkits in both ACPI
  firmware routines and in a PCI expansion card ROM.

78
Virtualization Attacks on BIOS

• Virtualization viruses
• e.g. Blue Pill, run whole OS as a virtual
  machine, some physical RAM is invisible,
  rootkit claimed impossible to detect code
  released by Joanna Rutkowska
  c. 2010

79
SMM mode Viruses?

16-bit insecure mode

• SMI Handlers part of BIOS
• runs in special System Management Mode

80
SMI Handlers

• SMI Handlers part of BIOS, used for
• invented to manage CPU temperature, fan control
  etc
• also used for emulating hardware such as floppy
  disk
• Security
• runs in special System Management Mode (SMM)
• super-privileged, very similar to ring 0
• 16-bit yet able to access 4G of RAM
• can access all I/O ports and peripherals
• implemented through a System Management Interrupt
  (SMI)
• triggered by a physical PIN on the CPU socket
• transitions next slide

81
x86 CPU transitions w.r.t. SMI mode Duflot
et al.

16-bit start-up
32-bit
switched on by a PIN on the CPU socket, 386 and
above
82
Improved BIOS

• BIOS is not modular.
• In some recent computers the BIOS has two parts
• 1. BIOS boot block, cannot be updated,
• in ROM preferably
• checks the integrity of the second block 2.
• for this it can cooperate with special chip
  (Trusted Platform chip)
• has recovery mechanisms
• dual BIOS, restore last BIOS etc..
• 2. Main block, can be updated
• in Flash memory

83
2006 Bill Gates / Intel

• If we think about boot, we're finally moving away
  from the old BIOS to this UEFI interface
• gives us new flexibility and capability, and
  it's got a rich API set to build on

84
New Vocab
EFI, Extensible Firmware Interface, UEFI
Unified EFI An industry group (Intel, Lenovo,
Microsoft etc etc) PI Platform Initialization
process and specs..

85
Key Features of EFI

• authenticated BIOS updates using digital
  signatures
• protections against changing the BIOS already
  installed
• modular design, with added functionality in BIOS,
  
• for example support of FAT files system in
  firmware through EFI drivers
• Reading NIST BIOS protection guidelines
  SP800-147

86
Improved EFI BIOS and Boot cf. NIST

Checks the digital signature, root of trust
87
Optional Reading A Tale of Two Standards

88

• Enterprise Remote IT Management

89
Couple AMT vPro

• AMT Active Management Technology software
  part.
• Works with HARDWARE Intel vPro support on CPU and
  motherboard and the network adapter.
• A very impressive set of out-of-band techniques
  to remotely connect to PCs, even without
  knowledge or permission of the OS and the user
  that physically controls the PC.
• Remote power up
• Remote configuration, including access to BIOS
• Encrypted network boot
• Programmable hardware-based network filters and
  alerts
• Remotely limit network traffic of infected PCs
• Persistent logs stored in protected hardware

90

• Intel Anti-Theft Technology
• (2010)

91
Statistics

• 10 of all laptops are stolen during 1 year
• 97 are never found / recovered source FBI

92
Intel Anti-Theft Technology 2010

• Tamper-resistant HARDWARE protections
• Allows encryption solutions to store and manage
  cryptographic keys in CPU hardware.
• Ability to disable your PC with a local or remote
  poison pill if the system is lost or stolen. The
  poison pill can then delete essential
  cryptographic keys in CPU hardware.
• The PC will refuse to boot
• works even if the OS is reimaged, the boot order
  is changed, a new hard-drive is installed, or the
  laptop is disconnected from the network.
• supports outgoing SMS (alert) and incoming SMS
  (poison pill) through an optional 3G card
  built-in.
• can display a message to the thief
• like laptop reported missing, 100 reward if you
  find it, call this number etc.
• Customize the policy to respond to events
• invalid login attempts
• failure to check-in to company network
• tamper detection
• Has a reactivation capacity restore to normal.
• Secondary long pass phrase to unlock
• Unlock code can be transmitted by phone by the
  companys IT service.

93

• Anti-Theft Software and Support/Server
  Infrastructure

94
Location Tracing of a PC

95
Key Functionalities iPad example

• An app which can be triggered remotely by the
  owner
• Display a messagesound for the thief
• Remote lock
• Remote wipe of all the data
• Use the iPad Camera to collect crucial evidence
• Tamper-proof application.

96
Remark PC versus iPad

• An app which can be triggered remotely by the
  owner
• Display a messagesound for the thief
• Remote lock
• Remote wipe of all the data
• Use the iPad Camera to collect crucial evidence
• Tamper-proof application.

Out of band channels / BIOS rootkitsnot needed
(cf. PCs) Apple is in controlTamper-proof OS
97
Another Example for iPad

an app which can be triggered remotely by the
owner
98
CompuTrace

• Computrace Track Locate Recover
• embedded in laptops and some expensive Dell
  workstations. One needs to pay a subscription
  with this company.
• intended to trace lost/stolen PCs without the
  knowledge of the thief
• for legal reasons, apparently only available in
  US,UK,Canada and AUS.

99
CompuTrace as a RootKit

• also known as a legitimate BIOS rootkit.
• upon activation it will HACK/MODIFY the Windows
  partition
• add a new service!
• modify several system files and the registry
• modify self-healing mechanisms such as
  Autochk.exe so it CANNOT be detected or
  repaired(!)
• can be enabled or disabled or killed
• in the BIOS, appears as a PCI device 19171234,
  can be enabled
• in theory cannot be reactivated
• can be hacked/subverted, cf. Sacco-Ortega
  attacks, BlackHat 2009,
• redirection of communications changing the
  URL/IP address
• lack of authentication of code, could be replaced
  by malicious code...
• Rootkit CAN be re-set to default settings and
  re-activated by software only
• maybe can download unauthorized code during
  updates?

100

• I/O Protection

101
In Both Unix and Windows NT

• I/O devices are usually NOT accessible in user
  mode!

protected mode
user space
driver
I/O device
IPC
process
kernel
shared RAM
102
Example

• In Linux,
• ONLY a process with effective UID 0 (and
  0root)
• can open TCP ports with numbers lt1024.

103
In Both Unix and Windows NT

• There are two main methods for accessing I/O
• mapping I/O to RAM,
• access as shared memory
• data written will be interpreted as commands
• dedicated I/O instructions,
• available only in the supervisor mode (!)

104
How Devices Communicate with Drivers?

• 3 techniques
• Programmed I/O periodic polling
• the I/O device, such as mouse, writes
  periodically some information at a certain
  location
• Interrupt-driven I/O
• uses hardware interrupts to tell the CPU data is
  here
• DMA Direct Memory Access,
• independent of CPU, but it can be stalled when
  transfer is active
• CPU controls the DMA
• there are complications because of CPU cache!
• usually CPU will flush the cache manually
  complicated

105

• OS Design

106
Kernel space vs. User space

• Two separate memory zones.
• Kernel space the OS kernel, some kernel
  extensions, some device drivers
• run in the most privileged CPU mode, system mode.
• this memory usually cannot be swapped out.
• User space, Userland other parts of the OS that
• run as processes or services/daemons in the user
  mode.
• I/O and components
• manipulating the filesystem
• shell
• Windows
• system processes will be running as system, so
  user space is a confusing name!
• user processes will be running as user.
• Depending on systems we can have system root
  super-user administrator or all these will be
  distinct...

107
Kernel Space vs. User Space
??
Process 1
Process 2
Process n
The Kernel
Hardware (disks, network interfaces, etc.)
108

• Kernel Design

109
Big Kernels vs. Micro Kernels

110
Big (Monolithic) Kernels

• The entire OS runs in system mode.
• Big kernel has all services
• file system,
• network services,
• device drivers, etc.
• Security all kernel code run in one address
  space and can directly affect each other.
• Example Linux 2.6 kernel 6 millions lines of
  code
• fast
• less robust, less secure
• Kernels with loadable kernel modules are still
  monolithic

111
Microkernels

• A minimal kernel which provides only the
  mechanisms needed to implement OS services,
• Kernel provides
• low-level memory space management,
• thread and process management,
• inter-process communication (IPC).
• Operating-system services are provided by
  user-mode server modules.
• device drivers,
• protocol stacks,
• file systems
• user-interface code.
• More secure(better achieves least privilege),
  more robust w.r.t. failures and bugs.
• Slower

112
Hybrid or Mixed

• Mix of both worlds

113
Windows NT family (NT,XP,Vista). A hybrid
kernel or a monolithic kernel structured like a
microkernel
114

• Trusted Path

115
Trusted Path

• One possible meaning (also used in Trusted
  Computing NGCB)
• a mechanism that provides confidence that the
  user is communicating with the right
  program/process
• attackers should not be able to
• initiate the communication process
• snoop on it / modify it
• defense against fake login programs.
• In other words something close to an
  unspoofable and incorruptible channel (for a
  process in question).

116
Trusted Path and DRM

• The dream of Hollywood studios
• A graphics card that decrypts video directly with
  AES-128, so that high-quality video cannot be
  captured
• Implemented in Windows Vista

117
Secure Attention Key

• Def a special key combination to be entered
  before a login screen is presented.
• Windows NT, XP and better CtrlAltDel
• Linux Ctrl-Alt-Pause or the SysRq-K

118
WinLogon Security

• Security
• Remark Users can be instructed to report login
  prompts that appear without having pressed this
  key combination.
• It is certainly an attack on their system!

119
WinLogon Security

• Windows NT is designed so that only the WinLogon
  process, a trusted system process, can receive
  notification of this keystroke combination.

120
How?

• only the WinLogon process can receive this
  keystroke
• The kernel remembers the Process ID of this
  process, and allows only that process to receive
  this notification.
• No software can intercept this call.
• Later, the WinLogon process will instruct GINA
  library (MSGINA.dll, Graphical Identification and
  Authentication) to bring the Windows Security
  Dialog
• It is possible to replace GINA with a third party
  software
• one that accepts smart card or other tokens (!)
• See HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows
  NT\CurrentVersion\Winlogon, a string named
  GinaDLL
• In VISTA, GINA was replaced by Credential
  Providers
• significantly increased flexibility in supporting
  multiple credential collection methods

121

• Security in the User Space

122
Security Mechanisms in the User Space

• User privileges (admin/not admin)
• Access Control
• Authentication
• Logging / Auditing
• Intrusion Detection

123
Logging

• Both normal and suspicious events, e.g.
• Every logon attempt
• Every time permissions are changed
• Network connection events
• Methods
• application logging,
• API hooking,
• system call interception,
• packet sniffing,
• Again, logging can be hidden and use WORM
  mechanisms (forensic logging).

124
Intrusion Detection

• Some also can and should be implemented by the OS
• A lot is done in Vista, a high level of
  paranoia in fact adopted here tilt bits (sth.
  abnormal is going on, false alarms most of the
  time, but the diffusion prime content will be
  prevented).

125

• Disturbing Questions
• and Virusology

126
Disturbing Questions

• The OS does have some file locks
• It does not allow one to change system files and
  things such as file meta-data easily.
• Can this be circumvented? Maybe.
• Idea, through locking the volume(possible) and
  directly accessing the disk, and directly
  communicating with the resources (for this one
  has to implement an impressive range of things,
  it is like implementing the OS from the scratch,
  not impossible but costly
• Some software, such as real-time disk defrag or
  real-time partition tools do need to have higher
  privileges than normal software.

127
Disturbing Questions

• The anti-virus software works in the user space?
• Not really (try to kill an anti_virus), but even
  if it has Kernel-level drivers there is a process
  to install it
• Q What prevents a virus from installing in the
  same way? With very high privileges the
  anti-virus needs to function?

128
Hacking Anti-virus Software

• Could one install a slightly modified anti-virus
  software?
• Defences The process is in fact pre-approved by
  Microsoft, installation is usually allowed by
  checking digital signatures of its key component
  a Kernel-level driver.
• But could we modify the anti-virus code on the
  fly during this installation process (during
  which some anti-virus code is promoted to a very
  high privilege)? Maybe

129
Jailing Anti-virus Software

• Could we put the anti-virus software in jail? Or
  just alter its communications with the central
  servers updates, status/virus reporting,
  redirection etc
• Maybe.

130

• Browser Design

131
Big (Monolithic) Browsers

• Legacy de facto dominant situation,
• since NCSA Mosaic program 1993
• Monolithic architecture
• initially, the browser kernel and the rendering
  engine were just single image (one exe file)
• later they became modular with dlls, plugins,
  JVM, etc.
• But from the point of view of the security
  nothing changed all code executed in one single
  protection domain.
• Examples IE7 under XP, Firefox 3, Safari 3.1.

132
One Single Domain

• Everything is run in one single protection domain
  at the users level of privilege, for example as
  admin.
• A single crash crashes everything
• Code that comes from the web runs locally at
  users level of privilege
• an un-patched vulnerability in the browser allows
  to run any code on the host machine, with the
  privilege level of the user.

133
One Single Domain But Which?

• This is very insecure if we run the browser as
  admin.
• But what is we run it from a restricted account?
  Is it OK?
• Example Vista can run IE7 in a protected mode
  which means it is run at a low-integrity level.
  It implements the Bibas principle of no
  write-up. Consequences
• The browser is unable to alter the system. ?
• BUT it can read the users files (spyware). ?

Remember Integrity and Confidentiality are two
totally independent dimensions.
134
Sandboxing - Example

• VMWare Browser Appliance
• A free Linux VM containing Firefox, that runs
  with the VMWare player (also free). After you
  use it to browse web, just delete it. And start
  again
• How cool is that
• Big drawback complete isolation, the user is
  NOT able AT ALL to read any of his own files (for
  example to publish his photos on the web)

135
IE8

• Does the same as IE7, except that each tab is run
  as a separate virtual machine.
• Still no protection of users data.

136
Google Chrome Architecture

• Divides the browser application into two
  protection domains
• Browser kernel runs with users privileges,
• Sandboxed and isolated multiple instances of the
  rendering engine run at very low web privilege
  level,
• Chrome is open source.
• And highly compatible with existing web sites,
  unlike many other existing modular highly
  secure browsers DarpaBrowser, Tahoma.

137
Chromium Browser Kernel

• Browser kernel responsible for
• mediating file and network access, like a
  firewall
• displaying bitmaps produced by rendering
  engines seen as black boxes.

138
Chromium Browser Kernel Privileges

• run at users privileges.
• run as a medium-integrity process under Vista,
  several privileges explicitly removed, starts
  with SID0
• as a result, it can be installed without an admin
  account (!). Maybe because it is not as
  dangerous as most other browsers

139
Problems

• Problems with Chrome
• it installs patches silently (very quick at
  updates, good point too)
• Java script cannot be disabled
• lack of many user and administrative controls
  (like zones)
• poor defaults, e.g. for cookies
• reveals all your passwords in seconds (nobody
  else allows that)
• embarrassments
• many serious and simple exploits were found
  already,
• and patched...

140
Rendering Engines

• multiple instances
• sandboxed and isolated
• each running with DEP and ASLR
• all run at very low web privilege level,
• at the lowest integrity level in Vista
• execute error and exploit-prone tasks of
• web parsing,
• Java script,
• etc.

141
How Does It Protect Our Files?

• As with IE7/8 under Vista, the rendering engines
  run as low integrity processes.
• So no write up is permitted.
• However Chrome also attempts to prevent them from
  reading up. How?

142
How Does It Protect Our Files!

• An engine, accessing URLs outside, is just
  totally unable of accessing local files file///
• However, of course, one can open a local web
  page.
• But only in another sandboxed and isolated
  rendering engine (!).

143
Small Technicality

• Memory isolation OK.
• But many file system isolation features will be
  ineffective if the file system is FAT32, not
  NTFS.
• Not because Vista is compromised or not able to
  further police the access (cf. reference
  monitor, complete mediation), but simply because
  of lack of support/implementation.

144

• Hardware Attacks on PCs

145
High-Level Categories

• Stealing data (removing hard drive, memory
  chips).
• Now hard drives can be encrypted.
• Memory still isnt.
• Hardware keyboard sniffers.
• Optical
• Acoustic / mechanical vibrations
• EM radiations. PS/2 vs. USB (two wires).
• Intercepting screen output.
• There are TEMPEST machines.
• Side channel attacks focusing on crypto.
• Acoustic attack on AES traditional DPA
  oscilloscope.
• CPU cache attacks on crypto (AES)

146
Quiz

• Can in Windows/Linux a process run by an
  administrator access the system/kernel memory?
• Explain what is virtual memory and paging?
• How one can make a dump of kernel memory?
• What is DEP? Which OS has it?
• Explain the protected/Kernel mode and user mode
  for CPUs.
• How can the DEP and the protected/Kernel mode be
  circumvented or attacked?

147
Quiz (2)

• How can we at the BIOS level make it difficult to
  modify the boot sector? (3 things).
• What is a monolithic kernel and why it is the
  least secure design?
• What is the architecture of Googles Chrome
  regarding the privileges to read and write files,
  access the network, and the screen?