Soma-notes - User contributions [en]

Scheduling

2007-12-02T00:37:01Z

Masha:

== QEMU ==
* Where does it fit in OS architecture?
* Simply a procdess, so: [Image 1 goes here]
* If a shell is running in QEMU, it is not seen from the regular terminal
* Quite analogous to the J(ava) V(irtual) M(achine)

== Virtual Machine Monitor ==
* What do you emulate?
** QEMU emulates ''everything'' (like PowerPC binaries for Intel x86 chip) [Image 2 goes here]
* If data coming in is the Linux kernel, it expects to be run in supervisor mode, so QEMU has to emulate supervisor mode (otherwise cannot process privileged instructions)
* If a program in user mode executes a privileged instruction, a software interrupt gets generated, and the kernel is called to look up the trap table
** Example: division by zero
* We would like to emulate any hardware we want; so, why not just dump code directly on the CPU without QEMU in-between?
** Cannot do this, because regular Linux kernel will catch the interrupts
*** One possible way to get around this is to take out privileged instructions from binaries (essentially rewrite them)

== Hypervisor ==
* The kernel's kernel [Image 3 goes here]

=== Ring Model ===
* Unix only has two rings: kernel = 0, user = 3 [Image 4 hoes here]
* If hypervisor runs in -1, we can run multiple operating systems on top of the hypervisor [Image 5 goes here]
* The hypervisor is part of the mechanism that prevents pirated games from playing on the Play Station 3
* Hypervisor does not really affect performance, because it is tacked onto the I/O part of system calls
* Translating memory access from applications in user spaces means switching to kernel (supervisor), and then again from supervisor to hypervisor
* If running multiple operating systems, hypervisor designates one operating system to be the host or root access
* "Server consolidation" - using machines to the best of their abilities to conserve power

=== "Blue Pill" ===
* When an attacker comes in, they have to run as a user process
* To hide, try to modify kernel code to camouflage processes
* Put security code in hypervisor - only good if attacker does not get there first
* Apparently, Windows kernel can actually tell if it has been virtuatlized, because there is one process that cannot be changed - the clock, so determine virtualization by checking the timing of I/O and interrupts
* "Halting problem"

== MMU ==
* How do we translate addresses? For some process, looking at address 2000 actually means looking at 8420
* Every instruction accessing memory has to perform this translation
* There exist tables that keep these - in page intervals (a pages is approximately a 4KB block)
* MMU needs a cache (very fast) to keep these tables
* MMU also requires a special kind of memory called associative memory (not like computers' main memory)
** Content-based access, not address-based
* TLB - translational lookaside buffer is the table with tags (directly on MMU), <64K
* If the TLB misses, the kernel gets called
* Locality of reference: for data and for code, can be spatial and temporal

Scheduling

2007-11-22T05:30:07Z

Masha: Initial outline commit

(Note: This is just a placeholder while I organize the information I have and create the images)

== QEMU ==
* Where does it fit in OS architecture?
* Simply a procdess, so: [Image 1 goes here]
* If a shell is running in QEMU, it is not seen from the regular terminal
* Quite analogous to the J(ava) V(irtual) M(achine)

== Virtual Machine Monitor ==
* What do you emulate?
** QEMU emulates ''everything'' (like PowerPC binaries for Intel x86 chip) [Image 2 goes here]
* If data coming in is the Linux kernel, it expects to be run in supervisor mode, so QEMU has to emulate supervisor mode (otherwise cannot process privileged instructions)
* If a program in user mode executes a privileged instruction, a software interrupt gets generated, and the kernel is called to look up the trap table
** Example: division by zero
* We would like to emulate any hardware we want; so, why not just dump code directly on the CPU without QEMU in-between?
** Cannot do this, because regular Linux kernel will catch the interrupts
*** One possible way to get around this is to take out privileged instructions from binaries (essentially rewrite them)

== Hypervisor ==
* The kernel's kernel [Image 3 goes here]

=== Ring Model ===
* Unix only has two rings: kernel = 0, user = 3 [Image 4 hoes here]
* If hypervisor runs in -1, we can run multiple operating systems on top of the hypervisor [Image 5 goes here]
* The hypervisor is part of the mechanism that prevents pirated games from playing on the Play Station 3
* Hypervisor does not really affect performance, because it is tacked onto the I/O part of system calls
* Translating memory access from applications in user spaces means switching to kernel (supervisor), and then again from supervisor to hypervisor
* If running multiple operating systems, hypervisor designates one operating system to be the host or root access
* "Server consolidation" - using machines to the best of their abilities to conserve power

=== "Blue Pill" ===
* When an attacker comes in, they have to run as a user process
* To hide, try to modify kernel code to camouflage processes
* Put security code in hypervisor - only good if attacker does not get there first
* Apparently, Windows kernel can actually tell if it has been virtuatlized, because there is one process that cannot be changed - the clock, so determine virtualization by checking the timing of I/O and interrupts
* "Halting problem"

== MMU ==
* How do we translate addresses? For some process, looking at address 2000 actually means looking at 8420
* Every instruction accessing memory has to perform this translation
* There exist tables that keep these - in page intervals (a pages is approximately a 4KB block)
* MMU needs a cache (very fast) to keep these tables
* MMU also requires a special kind of memory called associative memory (not like computers' main memory)
** Content-based access, not address-based
* TLB - translational lookaside buffer is the table with tags (directly on MMU), <64K
* If the TLB misses, the kernel gets called
* Locality of reference: for data and for code, can be spatial and temporal

--[[User:Masha|Masha]] 00:30, 22 November 2007 (EST)

Proposal Meeting Schedule

2007-11-05T19:47:40Z

Masha: /* Thursday, Nov. 8th */

==Tuesday, Oct. 30th==

{| class="wikitable"
| 10:00 AM
|
|-
| 10:10 AM
| Yan Li
|-
| 10:20 AM
|
|-
| 10:30 AM
|
|-
| 10:40 AM
|
|-
| 10:50 AM
|
|-
| 2:30 PM
|
|-
| 2:40 PM
|
|-
| 2:50 PM
|
|-
| 3:00 PM
|
|-
| 3:10 PM
|
|-
| 3:20 PM
|
|}

==Wednesday, Oct. 31st==

{| class="wikitable"
| 10:30 AM
|
|-
| 10:40 AM
|
|-
| 10:50 AM
|
|-
| 11:00 AM
|
|-
| 11:10 AM
|
|-
| 11:20 AM
|
|-
| 11:30 AM
|
|-
| 11:40 AM
| Matthew Peyrard
|-
| 11:50 AM
|
|-
| 12:00 PM
| Neil Dickson
|-
| 12:10 PM
|
|-
| 12:20 PM
| Richard Gould
|}

==Thursday, Nov. 1st==

{| class="wikitable"
| 1:30 PM
| David Tremayne (if someone needs this slot feel free to remove it and add yourself. this is just for receiving advice before a clear proposal is made)
|-
| 1:40 PM
|
|-
| 1:50 PM
|
|-
| 2:00 PM
|
|-
| 2:10 PM
| yini he
|-
| 2:20 PM
|
|}

==Monday, Nov. 5th==

{| class="wikitable"
| 2:40 PM
|
|-
| 2:50 PM
|
|-
| 3:00 PM
|
|-
| 3:10 PM
|
|-
| 3:20 PM
|
|-
| 3:30 PM
|
|-
| 3:40 PM
|
|-
| 3:50 PM
|}

==Tuesday, Nov. 6th==

{| class="wikitable"
| 10:00 AM
| Adam Krohn
|-
| 10:10 AM
| Dmitrii Miyusov
|-
| 10:20 AM
| Terry Worona
|-
| 10:30 AM
| David Tremayne
|-
| 10:40 AM
| Kevin McNally
|-
| 10:50 AM
| Joshua Tessier
|-
| 2:30 PM
|
|-
| 2:40 PM
| Adam Becevello
|-
| 2:50 PM
|
|-
| 3:00 PM
|
|-
| 3:10 PM
| Sean Brown
|-
| 3:20 PM
| Polina Vinogradova
|}

==Wednesday, Nov. 7th==

{| class="wikitable"
| 10:30 AM
| Kenneth Chan
|-
| 10:40 AM
| Alexander Beauvais
|-
| 10:50 AM
| Adrian Batos Parac
|-
| 11:00 AM
| Dan Edmunds
|-
| 11:10 AM
| Adam McNamara
|-
| 11:20 AM
| Ian Armstrong
|-
| 11:30 AM
| Nicholas O'Hara
|-
| 11:40 AM
| Geoffrey Johnson
|-
| 11:50 AM
| Irwin Zaid
|-
| 12:00 PM
| Simon Belanger
|-
| 12:10 PM
| Shachar Avni
|-
| 12:20 PM
| Roy Hooper
|}

==Thursday, Nov. 8th==

{| class="wikitable"
| 1:00 PM
|
|-
| 1:10 PM
|
|-
| 1:20 PM
|
|-
| 1:30 PM
| Nataly Hashem
|-
| 1:40 PM
| Seyamind Alkadhi
|-
| 1:50 PM
| Rajinder Wasson
|-
| 2:00 PM
| Bryan Mann-Lewis
|-
| 2:10 PM
| Andrew Yuill
|-
| 2:20 PM
| Matthew O'Hara
|-
| 2:30 PM
| Michael Rowe
|-
| 2:40 PM
|
|-
| 2:50 PM
|
|-
| 3:00 PM
|
|-
| 3:10 PM
| Maria Krol
|-
| 3:20 PM
| Jeff Snell
|}

Proposal Meeting Schedule

2007-11-05T19:47:30Z

Masha: /* Tuesday, Nov. 6th */

Proposal Meeting Schedule

2007-11-05T19:47:12Z

Masha: /* Thursday, Nov. 8th */

==Tuesday, Oct. 30th==

{| class="wikitable"
| 10:00 AM
|
|-
| 10:10 AM
| Yan Li
|-
| 10:20 AM
|
|-
| 10:30 AM
|
|-
| 10:40 AM
|
|-
| 10:50 AM
|
|-
| 2:30 PM
|
|-
| 2:40 PM
|
|-
| 2:50 PM
|
|-
| 3:00 PM
|
|-
| 3:10 PM
|
|-
| 3:20 PM
|
|}

==Wednesday, Oct. 31st==

{| class="wikitable"
| 10:30 AM
|
|-
| 10:40 AM
|
|-
| 10:50 AM
|
|-
| 11:00 AM
|
|-
| 11:10 AM
|
|-
| 11:20 AM
|
|-
| 11:30 AM
|
|-
| 11:40 AM
| Matthew Peyrard
|-
| 11:50 AM
|
|-
| 12:00 PM
| Neil Dickson
|-
| 12:10 PM
|
|-
| 12:20 PM
| Richard Gould
|}

==Thursday, Nov. 1st==

{| class="wikitable"
| 1:30 PM
| David Tremayne (if someone needs this slot feel free to remove it and add yourself. this is just for receiving advice before a clear proposal is made)
|-
| 1:40 PM
|
|-
| 1:50 PM
|
|-
| 2:00 PM
|
|-
| 2:10 PM
| yini he
|-
| 2:20 PM
|
|}

==Monday, Nov. 5th==

{| class="wikitable"
| 2:40 PM
|
|-
| 2:50 PM
|
|-
| 3:00 PM
|
|-
| 3:10 PM
|
|-
| 3:20 PM
|
|-
| 3:30 PM
|
|-
| 3:40 PM
|
|-
| 3:50 PM
|}

==Tuesday, Nov. 6th==

{| class="wikitable"
| 10:00 AM
| Adam Krohn
|-
| 10:10 AM
| Dmitrii Miyusov
|-
| 10:20 AM
| Terry Worona
|-
| 10:30 AM
| David Tremayne
|-
| 10:40 AM
| Kevin McNally
|-
| 10:50 AM
| Joshua Tessier
|-
| 2:30 PM
| Maria Krol
|-
| 2:40 PM
| Adam Becevello
|-
| 2:50 PM
| Jeff Snell
|-
| 3:00 PM
|
|-
| 3:10 PM
| Sean Brown
|-
| 3:20 PM
| Polina Vinogradova
|}

==Wednesday, Nov. 7th==

{| class="wikitable"
| 10:30 AM
| Kenneth Chan
|-
| 10:40 AM
| Alexander Beauvais
|-
| 10:50 AM
| Adrian Batos Parac
|-
| 11:00 AM
| Dan Edmunds
|-
| 11:10 AM
| Adam McNamara
|-
| 11:20 AM
| Ian Armstrong
|-
| 11:30 AM
| Nicholas O'Hara
|-
| 11:40 AM
| Geoffrey Johnson
|-
| 11:50 AM
| Irwin Zaid
|-
| 12:00 PM
| Simon Belanger
|-
| 12:10 PM
| Shachar Avni
|-
| 12:20 PM
| Roy Hooper
|}

==Thursday, Nov. 8th==

{| class="wikitable"
| 1:00 PM
|
|-
| 1:10 PM
|
|-
| 1:20 PM
|
|-
| 1:30 PM
| Nataly Hashem
|-
| 1:40 PM
| Seyamind Alkadhi
|-
| 1:50 PM
| Rajinder Wasson
|-
| 2:00 PM
| Bryan Mann-Lewis
|-
| 2:10 PM
| Andrew Yuill
|-
| 2:20 PM
| Matthew O'Hara
|-
| 2:30 PM
| Michael Rowe
|-
| 2:40 PM
|
|-
| 2:50 PM
|
|-
| 3:00 PM
|
|-
| 3:10 PM
| Maria Krol
|-
| 3:20 PM
| Jeffrey Snell
|}