Compare commits

..

3 Commits

Author SHA1 Message Date
4d16bc39ad
fix some things in CHERI article 2023-05-29 13:21:06 +01:00
d66796a3ef
add cv artifact 2023-05-29 13:19:10 +01:00
ee5685589f
remove gh actions 2023-05-29 13:18:47 +01:00
3 changed files with 2 additions and 41 deletions

View File

@ -1,39 +0,0 @@
# This is a basic workflow to help you get started with Actions
name: cv-build
# Controls when the workflow will run
on:
# Triggers the workflow on push or pull request events but only for the "master" branch
push:
branches: [ "master" ]
paths:
- cv/**
# Allows you to run this workflow manually from the Actions tab
workflow_dispatch:
# A workflow run is made up of one or more jobs that can run sequentially or in parallel
jobs:
# This workflow contains a single job called "build"
build:
runs-on: ubuntu-latest
steps:
- name: Set up Git repository
uses: actions/checkout@v2
- name: Compile LaTeX document
uses: xu-cheng/latex-action@v2
with:
working_directory: cv
root_file: main.tex
- name: Move built .pdf
run: |
mv cv/main.pdf ./static/cv.pdf
- name: Commit built .pdf
uses: EndBug/add-and-commit@v9
with:
add: 'cv.pdf'
author_name: 'Jack Bond-Preston'
author_email: 'jackbondpreston@outlook.com'
message: '[github action] update cv.pdf'

View File

@ -117,13 +117,13 @@ $ ./ptrs_as_numbers
*(7fff98640c28)=9999
```
yikes! now, when you start messing with pointers like this, you're bound to run into a bunch of undefined behaviour. but C programmers write undefined behaviour all the time (and not always by accident), and my computer executes this program fine without complaining at all. doesn't it feel a bit weird that we can take a pointer to `arr[0]` and modify it to load `secret`? they're not even part of the same array...
yikes! now, when you start messing with pointers like this, you're bound to run into a bunch of undefined behaviour. but C programmers write undefined behaviour all the time (and not always by accident), and my computer executes this program fine without complaining at all. doesn't it feel a bit weird that we can take a pointer to `arr[0]` and modify it to load `magic`? they're not even part of the same array...
## introducting capabilities
CHERI introduces capabilities, which can be thought of as an extension to pointers. they still store an address of something we care about, but they have extra information too! in a 64-bit system, a pointer would typically be a 64-bit value (as dicussed previously). the corresponding capability in a CHERI platform is 128 bits (or 129 bits if you look at it a certain way, more about that later).
as you might have guessed, this "extra information" takes up 64 bits of the capability. bits are assigned to three key pieces of metadata: *bounds*, *permissions*, and *object type*. there is also an additional 1-bit _tag_ which is stored out-of-band: it is not a 129-bit value - instead each 128-bit capability can be thought of as being associated with a 1-bit validity tag. the architecture manages this association for us. the diagram below is provided as a rough overview of this. note that it is not to scale.
as you might have guessed, this "extra information" takes up extra bits of the capability (how much is actually a little complicated - we will touch on that). bits are assigned to three key pieces of metadata: *bounds*, *permissions*, and *object type*. there is also an additional 1-bit _tag_ which is stored out-of-band: it is not a 129-bit value - instead each 128-bit capability can be thought of as being associated with a 1-bit validity tag. the architecture manages this association for us. the diagram below is provided as a rough overview of this. note that it is not to scale.
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1920 314"><defs><style>.prefix__c{fill:none;stroke:#fcfcfc;stroke-linecap:square;stroke-miterlimit:10;stroke-width:3px}.prefix__f,.prefix__g{fill:#fcfcfc}.prefix__f{font-family:Source Code Pro;font-size:20px}</style></defs><g id="prefix__a"><path fill="#0c1114" d="M0 0h1920v314H0z"/><text transform="translate(101.86 232.41)" font-family="Source Code Pro" font-weight="700" fill="#fcfcfc" font-size="24"><tspan x="0" y="0">int *x (capability)</tspan></text><text transform="translate(1205.97 232.1)" font-family="Source Code Pro" fill="#fcfcfc" font-size="24"><tspan x="0" y="0">0x0000010000000004</tspan></text><path class="prefix__c" d="M1016 261v18.5M1656 261v18.5M1016 279.5h640"/><text class="prefix__f" transform="translate(1293.78 296.33)"><tspan x="0" y="0">address</tspan></text><path class="prefix__c" d="M700 191.5V173M1020 191.5V173M700 173h320"/><text class="prefix__f" transform="translate(823.78 167.74)"><tspan x="0" y="0">bounds</tspan></text><path class="prefix__c" d="M554 260.34v18.5M704 260.34v18.5M554 278.84h150"/><text class="prefix__f" transform="translate(562.78 295.68)"><tspan x="0" y="0">object type</tspan></text><g><path class="prefix__c" d="M391.89 191.56v-18.5M541.89 191.56v-18.5M391.89 173.06h150"/></g><text class="prefix__f" transform="translate(400.67 167.8)"><tspan x="0" y="0">permissions</tspan></text><text class="prefix__f" transform="translate(304.67 31.07)"><tspan x="0" y="0">tag (out-of-band)</tspan></text><g><path class="prefix__c" d="M391.33 55.92v-18.5M421.33 55.92v-18.5M391.33 37.42h30"/></g></g><g id="prefix__b"><path class="prefix__g" d="M1651.66 205.93v40h-632v-40h632m4-4h-640v48h640v-48z"/><path class="prefix__g" d="M1016 206v40H704v-40h312m4-4H700v48h320v-48z"/><path class="prefix__g" d="M700 206v40H558v-40h142m4-4H554v48h150v-48z"/><path class="prefix__g" d="M554 206v40h-12v-40h12m4-4h-20v48h20v-48z"/><path class="prefix__g" d="M538 206v40H396v-40h142m4-4H392v48h150v-48zM418.5 70v40h-22V70h22m4-4h-30v48h30V66z"/></g></svg>

BIN
cv.pdf Normal file

Binary file not shown.