Kernel-Level Programming: Entering Ring Naught

Plan for Today Review (Exam 1 Questions) Milestones in Computing Building a Kernel 1 Reminder: PS4 (part 1) is out now. If you want to have more time to work on your project idea instead of PS4, need to let me know this week. Everyone should have received an email with the recorded results for PS2, PS3, and Exam 1.

No Exam 2, 30 Final Instead, 2 Another Assignment, 1 March 20- 21, 14 March 25- 27, 37 Near End of Semester, 11 Took it already!, 1 Exam2 2

No Exam 2, 30 Final Instead, 2 Another Assignment, 1 March 20- 21, 14 March 25- 27, 37 Near End of Semester, 11 Took it already!, 1 Exam2 3 Exam 2 will be out March 25 and due March 27 (12:25pm)

Talk After Class Today! 4 Cyber War, Cyber Peace, Stones, and Glass Houses Gary McGraw, CTO Cigital 2:00 PM Rice Hall 130

6 “What is significant about the bakery algorithm is that it implements mutual exclusion without relying on any lower-level mutual exclusion. Assuming that reads and writes of a memory location are atomic actions, as previous mutual exclusion algorithms had done, is tantamount to assuming mutually exclusive access to the location. So a mutual exclusion algorithm that assumes atomic reads and writes is assuming lower-level mutual exclusion. Such an algorithm cannot really be said to solve the mutual exclusion problem. Before the bakery algorithm, people believed that the mutual exclusion problem was unsolvable--that you could implement mutual exclusion only by using lower-level mutual exclusion.”Communications of the ACM, August 1974 (2 pages) We will explore this next Tuesday!

What are the advantages/disadvantages of hardware-based memory isolation over software-based memory isolation? 7

8 Hardware Memory Isolation a[i] = x mem.rs

9 Hardware Memory Isolation STR r0, [r1] a[i] = x compiler assembler rustc as 0100101101011… mem.rs mem

10 Hardware Memory Isolation STR r0, [r1] a[i] = x compiler assembler rustc as 0100101101011… mem.rs mem process running code gash> mem loader

11 Hardware Memory Isolation STR r0, [r1] a[i] = x WRITE 0x57283952, 0x413024 LogicalAddress Segmentation Unit LinearAddress Paging Unit PhysicalAddress Memory compiler assembler rustc as 0100101101011… mem.rs mem process running code gash> mem loader

12 Hardware Memory Isolation STR r0, [r1] a[i] = x WRITE 0x57283952, 0x413024 compiler assembler rustc as 0100101101011… mem.rs mem process running code gash> mem loader LogicalAddress Segmentation Unit LinearAddress Paging Unit PhysicalAddress Memory FAIL!

Hardware Memory Protection 13 Page Table + L1 Index

15 Software-Based Memory Isolation? STR r0, [r1] a[i] = x WRITE 0x57283952, 0x413024 compiler assembler rustc as 0100101101011… mem.rs mem process running code gash> mem loader LogicalAddress Segmentation Unit LinearAddress Paging Unit PhysicalAddress Memory FAIL!

16 Software-Based Memory Isolation …lots of code… STR r0, [r1] a[i] = x WRITE 0x57283952, 0x413024 compiler assembler rustc 0100101101011… mem.rs mem process running code gash> mem loader LogicalAddress Segmentation Unit LinearAddress Paging Unit PhysicalAddress Memory

17 Software-Based Memory Isolation …lots of code… STR r0, [r1] a[i] = x WRITE 0x57283952, 0x413024 compiler assembler rustc 0100101101011… mem.rs mem process running code gash> mem loader LogicalAddress Segmentation Unit LinearAddress Paging Unit PhysicalAddress Memory fn main() { let mut a = [0, 1, 2, 3]; let i = 6; a[i] = 7; } > rustc oob.rs > ./oob task '<main>' failed at 'index out of bounds: the len is 4 but the index is 6', oob.rs:5

18 rustc -S oob.rsLtmp4: … movq $6, -40(%rbp) movq -40(%rbp), %rcx cmpq $4, %rcx setae %dl testb $1, %dl movq %rdi, -48(%rbp) movq %rax, -56(%rbp) movq %rcx, -64(%rbp) jne LBB0_2 movq -56(%rbp), %rax movq -64(%rbp), %rcx movq $7, (%rax,%rcx,8) addq $64, %rsp popq %rbp ret LBB0_2: leaq _str1253(%rip), %rsi movabsq $5, %rdx movabsq $4, %r8 movq -64(%rbp), %rcx callq __ZN8unstable4lang17fail_bounds_check19h71a9f1 .cfi_endproc

19 Software-Based Memory Isolation …lots of code… STR r0, [r1] a[i] = x jne LBB0_2 compiler assembler rustc 0100101101011… mem.rs mem process running code gash> mem loader LogicalAddress Segmentation Unit LinearAddress Paging Unit PhysicalAddress Memory FAIL!

20 Software-Based Memory Isolation …lots of code… STR r0, [r1] a[i] = x jne LBB0_2 compiler assembler rustc 0100101101011… mem.rs mem process running code gash> mem loader LogicalAddress Segmentation Unit LinearAddress Paging Unit PhysicalAddress Memory FAIL! What if you aren’t starting with source code in a type-safe language?

21 Software-Based Memory Isolation STR r0, [r1] a[i] = x jne LBB0_2 compiler assembler rustc 0100101101011… mem.rs mem process running code gash> mem loader LogicalAddress Segmentation Unit LinearAddress Paging Unit PhysicalAddress Memory FAIL!transformer / loader

Which is more “expensive”? Hardware-Based Memory Isolation Transistors + wires OS sets up page permissions, loads programs Software-Based Memory Isolation Trusted compiler/loader Statically safe: no runtime cost! 23

Entering the Kernel 24 Photo: RDTaken

Hello World? 25 fn main() { println("Hello?"); }

1. What’s the difference between a programming language and an operating system? 26

27 Image: flickr cc: Ruben Alexander

Which came first? • Early programming languages did not run on an Operating System – Turing’s language, Church’s Lambda Calculus – IPL/Lisp, FLOW-MATIC, etc. • Early operating systems were not written in programming languages 29

Programming Language Operating System 30

Programming Language • Mostly a precise way for humans to describe programs • Provides abstractions of (abstract) machine resources • Associated programs like compilers translate into a program for machines to execute • Modern programming languages usually depend on an underlying OS Operating System • A program that runs on some hardware • Provides abstractions for (real) machine resources • Manages sharing of machine resources • Modern operating systems are mostly implemented in C (arguably a programming language) and assembly 31

Kernel Programming in Rust 32 #[no_std]; fn main() { println("Hello?"); }

Kernel Programming in Rust 33 #[no_std]; fn main() { println("Hello?"); } > rustc hello.rs hello.rs:4:5: 4:12 error: unresolved name `println`. hello.rs:4 println("Hello?"); ^~~~~~~ error: aborting due to previous error

Printing is For The Weak! 34 #[no_std]; fn main() { let mut a = [0, 1, 2, 3]; let i = 6; a[i] = 7; }

Main is For The Weak! 35 #[no_std]; fn main() { let mut a = [0, 1, 2, 3]; let i = 6; a[i] = 7; } > rustc oob1.rs error: requires `start` lang_item

36 #[no_std]; #[start] fn main(_: int, _: **u8) -> int { let mut a = [0, 1, 2, 3]; let i = 6; a[i] = 7; }

37 #[no_std]; #[start] fn main(_: int, _: **u8) -> int { let mut a = [0, 1, 2, 3]; let i = 6; a[i] = 7; } gash> rustc oob2.rs oob2.rs:4:1: 9:2 error: not all control paths return a value oob2.rs:4 fn main(_: int, _: **u8) -> int { oob2.rs:5 let mut a = [0, 1, 2, 3]; oob2.rs:6 let i = 6; oob2.rs:7 oob2.rs:8 a[i] = 7; oob2.rs:9 } error: aborting due to previous error

38 #[no_std]; #[start] fn main(_: int, _: **u8) -> int { let mut a = [0, 1, 2, 3]; let i = 6; a[i] = 7; return 0; }

39 rustc -S oob.rsLtmp4: … movq $6, -40(%rbp) movq -40(%rbp), %rcx cmpq $4, %rcx setae %dl testb $1, %dl movq %rdi, -48(%rbp) movq %rax, -56(%rbp) movq %rcx, -64(%rbp) jne LBB0_2 movq -56(%rbp), %rax movq -64(%rbp), %rcx movq $7, (%rax,%rcx,8) addq $64, %rsp popq %rbp ret LBB0_2: leaq _str1253(%rip), %rsi movabsq $5, %rdx movabsq $4, %r8 movq -64(%rbp), %rcx callq __ZN8unstable4lang17fail_bounds_check19h71a9f1 .cfi_endproc

40 #[no_std]; #[start] fn main(_: int, _: **u8) -> int { let mut a = [0, 1, 2, 3]; let i = 6; a[i] = 7; return 0; } bash-3.2$ rustc oob3.rs oob3.rs:8:5: 8:8 error: requires `fail_bounds_check` lang_item oob3.rs:8 a[i] = 7; ^~~

41 #[no_std]; extern "rust-intrinsic" { fn abort() -> !; } #[no_mangle] pub extern fn rust_stack_exhausted() { unsafe { abort() } } #[lang="fail_bounds_check"] pub fn fail_bounds_check(_: *i8, _: uint, _: uint, _: uint) { unsafe { abort() } } #[start] fn main(_: int, _: **u8) -> int { let mut a = [0, 1, 2, 3]; let i = 6; a[i] = 7; return 0; }

42 #[no_std]; extern "rust-intrinsic" { fn abort() -> !; } #[no_mangle] pub extern fn rust_stack_exhausted() { unsafe { abort() } } #[lang="fail_bounds_check"] pub fn fail_bounds_check(_: *i8, _: uint, _: uint, _: uint) { unsafe { abort() } } #[start] fn main(_: int, _: **u8) -> int { let mut a = [0, 1, 2, 3]; let i = 6; a[i] = 7; return 0; } gash> rustc oob4.rs gash> ./oob4 Illegal instruction: 4

43 #[no_std]; extern "rust-intrinsic" { fn abort() -> !; } #[no_mangle] pub extern fn rust_stack_exhausted() { unsafe { abort() } } #[lang="fail_bounds_check"] pub fn fail_bounds_check(_: *i8, _: uint, _: uint, _: uint) { unsafe { abort() } } #[start] fn main(_: int, _: **u8) -> int { let mut a = [0, 1, 2, 3]; let i = 2; a[i] = 7; return 0; } gash> rustc oob5.rs gash> ./oob5 gash>

IronKernel 44 Kevin Broderick, Alex Lamana, Zeming Lin, John Stevans, Wil Thomason

Building a Kernel 45 #[no_std] Remove everything from Rust that depends on OS: everything that uses system calls rust-core Library that doesn’t depend on OS.

// Copyright 2014 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. use fail::abort; use mem::replace; pub enum Option<T> { Some(T), None } impl<T> Option<T> { /// Returns true if the option contains a `Some` value pub fn is_some(&self) -> bool { match *self { Some(_) => true, None => false } } core/option.rs 46 /// Convert from Òption<T>` to Òption<&T>` pub fn as_ref<'a>(&'a self) -> Option<&'a T> { match *self { Some(ref x) => Some(x), None => None } } /// Convert from Òption<T>` to Òption<&mut T>` pub fn as_mut<'a>(&'a mut self) -> Option<&'a mut T> { match *self { Some(ref mut x) => Some(x), None => None } } /// Return the value in an Òption` or call àbort` if it is `None`. pub fn get(self) -> T { match self { Some(x) => x, None => abort() } } /// Maps an Òption<T>` to Òption<U>` by applying a function to a contained value. pub fn map<U>(self, f: |T| -> U) -> Option<U> { match self { Some(x) => Some(f(x)), None => None } } /// Applies a function to the contained value or returns a default. pub fn map_or<U>(self, def: U, f: |T| -> U) -> U { match self { None => def, Some(t) => f(t) } } /// Take the value out of the option, leaving a `None` in its place. #[inline(always)] pub fn take(&mut self) -> Option<T> { replace(self, None) } } Why does normal Option type need OS?

47 https://github.com/mozilla/rust/blob/master/src/libstd/option.rs Almost all normal code relies on an underlying OS!

Building a Kernel 48 #[no_std] Remove everything from Rust that depends on OS: everything that uses system calls rust-core Library that doesn’t depend on OS. rustboot

Building a Kernel 52 #[no_std] Remove everything from Rust that depends on OS: everything that uses system calls rust-core Library that doesn’t depend on OS. rustboot Boot! IronKernel 32-bit ARM OS kernel that can print text on the screen (in many colors!), handle keyboard input (as long as you don’t press any “dangerous” keys

Kernel Programming 54 Development Machine (Ubuntu 64-bit x86 Linux) editors, file system, networ k, compilers Target Machine (32-bit ARM)

Kernel Programming 55 Development Machine (Ubuntu 64-bit x86 Linux) editors, file system, networ k, cross-compilers Target Machine (32-bit ARM) ARM binary

Kernel Programming 56 Development Machine (Ubuntu 64-bit x86 Linux) editors, file system, networ k, cross-compilers QEMU: Emulator (32-bit ARM) ARM binary

57 How the kernel is built: > rustc --emit-llvm mod.rs > llc -march=arm -mcpu=arm926ej-s mod.bc > arm-none-eabi-as mod.as > objcopy mod.o … mod.rs mod.bc mod.s mod.o kernel.bin rustc llc arm-none-eabi-as objcopyassembler naming convention: [processor]-[os]-[application binary interface]

58 How the kernel is built: > rustc --emit-llvm mod.rs > llc -march=arm -mcpu=arm926ej-s mod.bc > arm-none-eabi-as mod.as > objcopy mod.o … mod.rs mod.bc mod.s mod.o kernel.bin rustc llc arm-none-eabi-as objcopyassembler naming convention: [processor]-[os]-[application binary interface] Easy way: make run

60 *((addr + (i * 4)) as * mut u32) = val

61 Reminder: stay for Gary McGraw talk! Form PS4 Teams while you are waiting for Gary’s talk! A PS4 team can be any 3 people.

Kernel-Level Programming: Entering Ring Naught

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