# Level 8

## Problem

The elimination of `CheckBounds` node had been changed to:
- Assume `CheckBounds` node has two input operand node `index` and `length`.
    - Each of them have a type labeled with their range `[min, max]`. 
- When `index.min >= 0.0 && index.min < length.min`, the `CheckBounds` will be eliminated.

## Key Knowledge
- Bound Check Elimination based Out of Bound Access
    - CVE-2020-9802
        - [Exploitation of CVE-2020-9802: a JavaScriptCore JIT Bug](https://shxdow.me/cve-2020-9802/)
        - [JITSploitation I: A JIT Bug](https://googleprojectzero.blogspot.com/2020/09/jitsploitation-one.html)
        - [CVE-2020-9802 JSC CSE漏洞分析](https://www.anquanke.com/post/id/245946)
        - [CVE-2020-9802-WebKit JIT优化漏洞分析](https://xz.aliyun.com/t/8913)
    - `String.lastIndexOf` Off By One bug in V8
        - [Security: off by one in TurboFan range optimization for String.indexOf](https://issues.chromium.org/issues/40088942)
        - [Attacking Client-Side JIT Compilers, Page 76-86](https://i.blackhat.com/us-18/Wed-August-8/us-18-Gross-New-Trends-In-Browser-Exploitation-Attacking-Client-Side-JIT-Compilers.pdf#page=76)
    - Bound Check Elimination related Simplified Lowering Phase in V8
        - [浅析 V8-turboFan](https://kiprey.github.io/2021/01/v8-turboFan/#4-SimplifiedLoweringPhase)
    - Use this technique to corrupt array's length.
- Make JIT engine consider an unspeculated parameter as an integer
    - Use bitwise operations