MINIX3: A Reliable and Secure Operating System

MINIX3: A Reliable and Secure Operating System Andrew S. Tanenbaum and a team of students and programmers who actually did all the work Vrije Universiteit Amsterdam, The Netherlands

1

GOAL OF OUR WORK: BUILD A RELIABLE OS Tanenbaum’s definition of a reliable OS: “An operating system is said to be reliable when a typical user has never experienced even a single failure in his or her lifetime and does not know anybody who has ever experienced a failure.” In engineering terms, this is probably mean time to failure > 50 years I don’t think we are there yet 2

THE TELEVISION MODEL 1. You buy the television 2. You plug it in 3. It works perfectly for the next 10 years

3

THE COMPUTER MODEL (WINDOWS EDITION) 1. You buy the computer 2. You plug it in 3. You install service packs 1 through 9f 4. You install 18 new emergency security patches 5. You find and install 7 new device drivers 6. You install antivirus software 7. You install antispyware software 8. You install antihacker software (firewall) 9. You install antispam software 10. You reboot the computer 4

THE COMPUTER MODEL (2) 11. It doesn’t work 12. You call the helpdesk 13. You wait on hold for 30 minutes 14. They tell you to reinstall Windows

5

TYPICAL USER REACTION

The New York Times recently reported that 25% of computer users have gotten so angry at their computer that they physically hit it.

6

IS RELIABILITY SO IMPORTANT? •  Annoying •  Lost work •  But also think about –  Industrial control systems in factories –  Power grids –  Hospital operating rooms –  Banking and e-commerce servers –  Emergency phone centers –  Control software in cars, airplanes, etc.

7

IS THIS FEASIBLE? •  •  •  • 

We won’t find out if we don’t try Dutch Royal Academy gave me €2 million to try European Union gave me €2.5 million to give it a shot So, we’re trying

8

IS RELIABILITY ACHIEVABLE AT ALL? •  Systems can survive hardware failures! –  RAIDs can survive failed disks –  ECC memory can survive parity errors in memory –  TCP/IP can survive lost packets –  CD-ROM drives can correct many simultaneous errors

•  We need to be able to survive software failures, too

9

A NEED TO RETHINK OPERATING SYSTEMS •  Operating systems research need to be refocused –  We have nearly infinite hardware on PC-class machines –  Plenty of CPU cycles, RAM, bandwidth –  Current software has tons of (useless) features –  Consequently, the software is slow, bloated, and buggy

•  To achieve the TV model, future OSes, must be –  Small –  Simple –  Modular –  Reliable –  Secure –  Self-healing

10

BRIEF HISTORY OF OUR WORK •  •  •  •  •  •  •  •  •  •  • 

(1976) John Lions wrote a book on UNIX V6 (1979) AT&T released V7 and forbade books on it L (1985) I started to write a UNIX-like OS from scratch (1987) MINIX 1 + book for teaching OS classes released (1997) MINIX 2 (POSIX) & 2nd edition of book released (2000) MINIX 2 license changed to BSD (2004) MINIX 3: start of work making a reliable OS (2006) 3rd edition of book (2008) European grant (2010) Focus moved towards embedded systems (2013) MINIX 3.3.0 moves to NetBSD “compatibility” 11

THREE EDITIONS OF THE BOOK

1

2

3 12

INTELLIGENT DESIGN AS APPLIED TO OPERATING SYSTEMS

•  Microkernel (15,000 LoC vs. > 15 million for Linux) –  Bugs per 1000 LoC: Most S/W (1-10) –  MINIX 3 at least 15 kernel bugs; Linux has > 15,000 –  Drivers have 3-7x more bugs than rest of kernel –  About 70% of the code is drivers

•  Highly modular •  OS runs as multiple user-mode server processes

13

STEP 1: ISOLATE COMPONENTS •  Move all loadable modules out of the kernel –  includes all device drivers and file systems

•  Run each module as a separate process with POLA (Principle Of Least Authority)

14

STEP 2: ISOLATE I/O •  Isolate I/O devices •  Limit access to I/O ports •  Constrain DMA (needs hardware assistance)

15

STEP 3: ISOLATE COMMUNICATION •  •  •  • 

Limit interprocess communication Restrict kernel calls on a per component basis Restrict IPC on a ‘need-to-communicate’ basis Make sure faulty receiver cannot hang sender

16

ARCHITECTURE OF MINIX 3 Process Shell

User mode

FS 1

Disk

Kernel mode

Make

FS 2

TTY

...

User

...

Proc.

Net

Print

Servers

Other

...

Other

Drivers

Microkernel handles interrupts, processes, scheduling, IPC

17

USER-MODE DEVICE DRIVERS •  •  •  • 

Each driver runs as a user-mode process No superuser privileges Protected by the MMU Do not have access to I/O ports, privileged instrs

18

USER-MODE SERVERS •  Each server runs as a separate process •  Some key servers –  Virtual file server –  Actual file servers –  Process manager –  Memory manager –  Network server –  Reincarnation server

19

A SIMPLIFIED EXAMPLE: DOING A READ

1

Users

User

4

User mode

Servers

FS

Disk

2

Drivers

3 Kernel

File access when the block is in the FS cache 20

FILE SERVER (2)

1

Users

User

9

User mode

2 5

6 7,8

Disk

3 Notification

Servers

FS

Drivers

4 Kernel

File access when the block is NOT in the FS cache 21

REINCARNATION SERVER •  •  •  • 

Parent of all the drivers and servers When a driver or server dies, RS collects it RS checks a table for action to take e.g., restart it RS also pings drivers and servers frequently

22

DISK DRIVER RECOVERY

RS

User mode

4

1 5

User

FS

Servers

2 New driver

Disk driver

X

Users

3. Crash!

Drivers Kernel

System is self healing—this is how we hope to make it reliable 23

KERNEL RELIABILITY/SECURITY •  •  •  •  • 

Fewer LoC means fewer kernel bugs Small kernel (15,000 LoC) means reduced TCB NO foreign code (e.g., drivers) in the kernel Static data structures (no malloc in kernel) Moving bugs to user space reduces their power

24

IPC RELIABILITY/SECURITY •  Fixed-length messages (no buffer overruns) •  Rendezvous system was simple –  No lost messages –  No buffer management –  We had to add asynchronous messages

•  Interrupts and messages are unified

25

DRIVER RELIABILITY/SECURITY •  •  •  •  •  • 

Untrusted code: heavily isolated Bugs, viruses cannot spread to other modules Cannot touch kernel data structures Bad pointers crash only one driver; recoverable Infinite loops detected and driver restarted Restricted power to do damage (not superuser)

26

OTHER ADVANTAGES OF USER DRIVERS •  •  •  •  • 

Short development cycle Normal programming model No down time for crash and reboot Easy debugging Good flexibility

27

FAULT INJECTION EXPERIMENT •  •  •  •  •  •  •  • 

We injected 800,000 faults into each of 3 drivers Done on the binary drivers Examples, change src addr, dest addr, loop condition 100 faults were injected on each experiment Waited 1 sec to see if the driver crashed If no crash, inject another 100 faults and repeat The driver crashed in 18,038 trials The operating system NEVER crashed

28

PORT OF MINIX 3 TO ARM •  •  •  •  •  •  •  • 

Restructured source tree for multiple architectures Changed booting to support uboot for ARM Rewrote the low-level code dealing with hardware Changed code for context switching, paging, etc. Removed x86 segmentation code Imported NetBSD ARM headers and libraries Ported build.sh for cross-toolchain support Wrote drivers for SD card and other Beagle devices

29

EMBEDDED SYSTEMS

5 cm

BeagleBone Black

9 cm 30

CHARACTERISTICS Item

Beaglebone Black

31


CPU

Beaglebone Black

ARM v7

32


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

33


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

RAM

512 MB

34


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

RAM

512 MB

Flash

4 GB

35


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

RAM

512 MB

Flash

4 GB

Video

HDMI/1080p

36


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

RAM

512 MB

Flash

4 GB

Video

HDMI/1080p

GPIO pins

92

37


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

RAM

512 MB

Flash

4 GB

Video

HDMI/1080p

GPIO pins

92

Ethernet

10/100 Mbps

38


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

RAM

512 MB

Flash

4 GB

Video

HDMI/1080p

GPIO pins

92

Ethernet

10/100 Mbps

USB

1

39


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

RAM

512 MB

Flash

4 GB

Video

HDMI/1080p

GPIO pins

92

Ethernet

10/100 Mbps

USB

1

Open source

Yes 40


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

RAM

512 MB

Flash

4 GB

Video

HDMI/1080p

GPIO pins

92

Ethernet

10/100 Mbps

USB

1

Open source

Yes

Price (quantity 1)

$45 41


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

RAM

512 MB

Flash

4 GB

Video

HDMI/1080p

GPIO pins

92

Ethernet

10/100 Mbps

USB

1

Open source

Yes

Price (quantity 1)

$45

Raspberry Pi B+

42


Beaglebone Black

CPU

ARM v7

Clock

1 GHz

RAM

512 MB

Flash

4 GB

Video

HDMI/1080p

GPIO pins

92

Ethernet

10/100 Mbps

USB

1

Open source

Yes

Price (quantity 1)

$45

Raspberry Pi B+

ARM v6

43


Beaglebone Black

Raspberry Pi B+

CPU

ARM v7

ARM v6

Clock

1 GHz

700 MHz

RAM

512 MB

Flash

4 GB

Video

HDMI/1080p

GPIO pins

92

Ethernet

10/100 Mbps

USB

1

Open source

Yes

Price (quantity 1)

$45 44


Beaglebone Black

Raspberry Pi B+

CPU

ARM v7

ARM v6

Clock

1 GHz

700 MHz

RAM

512 MB

512 MB

Flash

4 GB

Video

HDMI/1080p

GPIO pins

92

Ethernet

10/100 Mbps

USB

1

Open source

Yes

Price (quantity 1)

$45 45


Beaglebone Black

Raspberry Pi B+

CPU

ARM v7

ARM v6

Clock

1 GHz

700 MHz

RAM

512 MB

512 MB

Flash

4 GB

None

Video

HDMI/1080p

GPIO pins

92

Ethernet

10/100 Mbps

USB

1

Open source

Yes

Price (quantity 1)

$45 46


Beaglebone Black

Raspberry Pi B+

CPU

ARM v7

ARM v6

Clock

1 GHz

700 MHz

RAM

512 MB

512 MB

Flash

4 GB

None

Video

HDMI/1080p

HDMI/1080p

GPIO pins

92

Ethernet

10/100 Mbps

USB

1

Open source

Yes

Price (quantity 1)

$45 47


Beaglebone Black

Raspberry Pi B+

CPU

ARM v7

ARM v6

Clock

1 GHz

700 MHz

RAM

512 MB

512 MB

Flash

4 GB

None

Video

HDMI/1080p

HDMI/1080p

GPIO pins

92

40

Ethernet

10/100 Mbps

USB

1

Open source

Yes

Price (quantity 1)

$45 48


Beaglebone Black

Raspberry Pi B+

CPU

ARM v7

ARM v6

Clock

1 GHz

700 MHz

RAM

512 MB

512 MB

Flash

4 GB

None

Video

HDMI/1080p

HDMI/1080p

GPIO pins

92

40

Ethernet

10/100 Mbps

10/100 Mbps

USB

1

Open source

Yes

Price (quantity 1)

$45 49


Beaglebone Black

Raspberry Pi B+

CPU

ARM v7

ARM v6

Clock

1 GHz

700 MHz

RAM

512 MB

512 MB

Flash

4 GB

None

Video

HDMI/1080p

HDMI/1080p

GPIO pins

92

40

Ethernet

10/100 Mbps

10/100 Mbps

USB

1

4

Open source

Yes

Price (quantity 1)

$45 50


Beaglebone Black

Raspberry Pi B+

CPU

ARM v7

ARM v6

Clock

1 GHz

700 MHz

RAM

512 MB

512 MB

Flash

4 GB

None

Video

HDMI/1080p

HDMI/1080p

GPIO pins

92

40

Ethernet

10/100 Mbps

10/100 Mbps

USB

1

4

Open source

Yes

No

Price (quantity 1)

$45 51


Beaglebone Black

Raspberry Pi B+

CPU

ARM v7

ARM v6

Clock

1 GHz

700 MHz

RAM

512 MB

512 MB

Flash

4 GB

None

Video

HDMI/1080p

HDMI/1080p

GPIO pins

92

40

Ethernet

10/100 Mbps

10/100 Mbps

USB

1

4

Open source

Yes

No

Price (quantity 1)

$45

$35 52

I ADMIT I WAS WRONG •  On 29 Jan 1992 I posted to comp.os.minix this: •  “Don`t get me wrong, I am not unhappy with LINUX. It will get all the people who want to turn MINIX in BSD UNIX off my back.” •  I Apologize. Now I do want to turn MINIX into BSD. It just took me 20 years to realize this.

53

MINIX 3 MEETS BSD

+

=

BSD Daemon is copyright 1988 by Marshall Kirk McKusick and is used with permission. 54

OR MAYBE

55

WHY BSD? •  •  •  •  •  •  •  •  • 

MINIX 3 didn’t have enough application software BSD is a proven, portable, quality product BSD has better code quality than Linux Pkgsrc handles packages better than what we had Thousands of excellent packages available Active community License compatibility Why NetBSD? Mostly due to its emphasis on portability 56

NETBSD FEATURES IN MINIX 3.3.0 •  •  •  •  •  •  •  • 

Clang/LLVM compiler NetBSD build system ELF file format Source code tree modeled on NetBSD Headers and libraries are from NetBSD X11 Pkgsrc works and builds 5040 NetBSD packages Nevertheless, it is built on MINIX 3 kernel & servers

57

NETBSD FEATURES MISSING IN MINIX 3.3.0 •  Kernel threads (we do have userland pthreads) •  Some system calls: –  All _LWP*, MSG*, SEM* calls –  CLONE –  Some GET, IOCTL calls –  KQUEUE, KTRACE –  VFORK –  Job control –  Some other minor calls

•  Nevertheless, we can build over 5000 packages 58

KYUA TESTS

Conclusion: 2139 out of 2651 passed (81%) 59

SYSTEM ARCHITECTURE Users Clang

Pkgsrc

(libc)

Pkg 1

…

Pkg n

UserLand (NetBSD)

Servers VFS

FS

MM

Rein carnat

… Drivers

Disk

Net

TTY

…

USB

OS (MINIX)

…

Microkernel (this is the only part running in kernel mode)

60

MINIX 3 ON THE THREE BEAGLE BOARDS

61

YOUR ROLE •  MINIX 3 is an open-source project •  I hope some of you will join and help us •  Things to do –  Add crucial missing system calls –  Port more packages (Java, a browser, etc.) –  Write the missing drivers for Beagle series –  Get it running on Raspberry Pi & other platforms –  Port Rump –  Port required libraries and then port a GUI

62

MINIX 3 IN A NUTSHELL •  •  •  •  •  •  • 

Microkernel reimplementation of NetBSD Fully open source with BSD license Highly compatible with NetBSD Supports both LLVM and gcc Uses NetBSD pkgsrc Over 5000 packages build Go get it at www.minix3.org and try it

63

POSITIONING OF MINIX •  •  •  •  • 

Show that multiserver systems are reliable Demonstrate that drivers belong in user mode High-reliability and fault-tolerant applications $50 single-chip, small-RAM laptops for 3rd world Embedded systems

64

FUTURE FEATURE: LIVE UPDATE •  Software is updated to: –  Fix bugs –  Improve performance –  Add new features

•  •  •  • 

Goal is to update OS to a new version w/o reboot Running processes must NOT be restarted New version of OS may have new data structures Lots of state in there: open files, timers,etc.

65

EXAMPLE OF HOW WOULD THIS WORK

User

Kernel

A

Apache running FreeBSD 10.1

A

Apache still running FreeBSD 10.2

•  Replace the OS while user processes are running •  Very difficult to do with BSD, Linux, Windows, etc.

66

LIVE UPDATE IN MINIX

User

A

User

MM

Kernel

Apache running Driver

Microkernel

FS 6.0

A

MM

Apache still running Driver

FS 7.0

Microkernel

67

HOW DO WE DO THE UPDATE? •  •  •  •  •  •  •  •  •  • 

Manager tells some process (e.g. Old-FS) to get ready Old-FS finishes its work and queues new work Manager creates New-FS process with new code LLVM puts tables inside New-FS listing its data objects New-FS contacts Old-FS and asks for state it needs The state is transferred one object at a time When all state is transferred, Third-FS is created It talks to New-FS and tries to recreate Old-FS If they agree New-FS becomes FS, else revert to Old-FS Like translating English to Dutch, then Dutch to English 68

HOW THE UPDATE WORKS

A

FS 6.0

Apache running

Old FS

Microkernel

69


A

Get ready

Apache running

FS 6.0

Microkernel

70


A

FS 6.0

Apache running FS 7.0

Microkernel

71


A

FS 6.0

Apache running I need variable x

FS G 7.0

Microkernel

72


A

FS 6.0

Apache running Here is variable x

FS 7.0

Microkernel

73


A

FS 6.0


FS ?

Microkernel

74


A

FS 6.0


I need variable x

FS ?

Microkernel

75


A

FS 6.0


Here is variable x

FS ?

Microkernel

76


A

FS 6.0


Are these the same?

FS ?

Microkernel

77


A


Microkernel

78

MUCH BETTER THAN KSPLICE •  •  •  • 

KSPLICE can handle only small security patches KSPLICE patches the running process Over time, crud accumulates in the process If the update fails, there is no recovery

79

OTHER USES OF LIVE UPDATE •  Enhanced security: –  Update the OS at a high rate to foil return-to-libc attacks –  Stop any attack that uses knowledge of memory layout –  Reduce exposure to information leakage attacks

•  Garbage collection in C (!) –  Only live data is copied over to the new version –  This can “fix” memory leaks (malloc but no free)

80

RESEARCH: FAULT INJECTION Inject fault?

Original unmodified basic block

Basic block with fault injected

This structure is created automatically by the LLVM compiler 81

NEW PROGRAM STRUCTURE

This can be optimized by patching the original binary to get any test without recompilation Overhead is 8%

82

MINIX 3 LOGO

•  Why a raccoon? –  Small –  Cute –  Clever –  Agile –  Eats bugs –  More likely to visit your house than a penguin 83

WEBSITE: www.minix3.org

84

DOCUMENTATION IS IN A WIKI •  Wiki.minix3.org •  You can help document the system

85

TRAFFIC TO WWW.MINIX3.ORG

Total visits to the main page since 2004: 3.1 million Actual downloads since 2007: 650,000 (from the log) 86

MINIX 3 GOOGLE NEWSGROUP

87

CONCLUSION •  •  •  •  •  •  •  • 

Current OSes are bloated and unreliable MINIX 3 is an attempt at a reliable, secure OS Kernel is very small (15,000 LoC) OS runs as a collection of user processes Each driver is a separate process Each OS component has restricted privileges Faulty drivers can be replaced automatically Live update is possible (not in current release)

88

SURVEY •  •  •  • 

Please download MINIX 3 from www.minix3.org Give it a try Fill out the survey on the main page We have had 650,000 downloads but we don’t know who they are or what they are doing •  We are trying to build a community

89

THE END

90

WEBSITE: www.minix3.org

91

92

MASTERS DEGREE AT THE VU •  •  •  •  • 

If you are interested in computer systems Look at our masters in parallel & distributed syst. Google me Look at my home page See video linked there or check out

pdcs.vu.nl 93

DISK PERFORMANCE

94

THE COST OF DRIVER RECOVERY •  We killed the Ethernet driver every Δt sec to simulate repeated driver crashes

Driver recovery takes about 360 msec 95

RESEARCH: MULTICORE CHIPS

Multicore chip

TCP

IP

Ether

Kernel

Core

•  •  •  •  •  • 

Network stack has components Chips may be heterogeneous Where to put each component? Experiments scaling frequencies Sometimes slower is faster! Sleep/wakeup is expensive

96

RESEARCH: NEW FILE SYSTEM--LORIS VFS

Naming

Cache

Logical

Physical

•  •  •  •  • 

Better reliabilty Better flexibility Handles heterogeneity better File rather than block oriented Uses checksums to detect corruption Introduces concept of a logical file (1 or more phys files spread or striped over possibly heterogeneous devices)

Driver

97