#Realm browser linux code
The OperandTypes holds metadata about the predicated types of loc1 and loc2.įigure 2 – The primary stages of JavaScript code goes through JS Can Go FAST This is merely adding loc1 with loc2 and saving the result in loc3.
#Realm browser linux Offline
For example, the expression “ a+b” we’ve mentioned earlier is translated to bytecode that consists of the following offline assembly opcodes:Īdd loc3, loc1, loc2, OperandTypes(126, 126) The LLInt will create bytecode that JSC can execute using the processor.
#Realm browser linux series
Lexing ( parser/Lexer.cpp) – The Lexer will break down our script into a series of tokens.Instruction ProcessingĮvery JS script we’ll execute via JSC will go through several phases: Additionally, JS is much more dynamic than C for instance, we don’t have to declare the arguments’ types when writing a new function. JS bytecode must go through another level of execution compared to a pre-compiled programming language, like C.īut, since our JS code is running in a virtual machine, we have less room for classic bugs because the virtual machine can do all sorts of checks during runtime and prevent these classic bugs from becoming a problem. The reason derives directly from the figure above. For example, running a native C function can be a lot faster than executing a similar function written in JS. It is well understood that each approach comes with its pros and cons.
Unlike code written in C, which we initially compile into native code that our processor can run, a virtual machine (JSC, for example) executes JS, and our processor executes the code of that virtual machine. JSC is the built-in JS engine for WebKit, meaning it handles each JS script we execute via our browser. “ WebKit is the web browser engine used by Safari, Mail, App Store, and many other apps on macOS, IOS and Linux.” – WebKit description from Goo the Owl: “Allow me to elaborate!” JavaScriptCore 101 Goo the Owl: “These gooey blobs are JavaScript instructions waiting to be executed.” Goo the Owl: “Well then, without further ado, let’s clone WebKit and enter the realm!” I’ll help you explore the realm – seems like a good use of my time.” Goo the Owl: “Oh nice! I heard about it from 91,500 places (0.43 seconds to search about it). Me: “I just got this new staff and figured I should explore this realm a bit.” Goo the Owl: “You can call me Goo, the all-knowing Owl. Goo(gle) the Owl: “Cloning the repository might be a good start.” But, not long ago, I received the magical staff of CodeQL, and now I feel confident enough to explore the realm I geared up and started my quest! Follow me on this immersive journey to learn the fundamentals of JSC and find some cool (old-school) bugs with CodeQL. Never have I dared to step foot in there since I thought I was way under-leveled to do so. I’ve always felt intimidated by the fog of war that was laying over the land of browser exploitation. Then, we describe how we developed a tailor-made CodeQL query that uncovers bad side effect modeling vulnerabilities, which could lead to RCE in JSC. In this blog post, we start by learning the fundamentals of JSC. The JSC engine is responsible for executing every line of JavaScript (JS) that needs to be executed, whenever we browse to a new website or simply send/receive emails.įinding vulnerabilities in JSC can be intimidating and, in some cases, complicated. JavaScriptCore (JSC) is the JavaScript engine used by Safari, Mail, App Store and many other apps in MacOs.
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