README

README

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-README for LuaJIT 2.1
----------------------
-
-LuaJIT is a Just-In-Time (JIT) compiler for the Lua programming language.
-
-Project Homepage: https://luajit.org/
-
-LuaJIT is Copyright (C) 2005-2023 Mike Pall.
-LuaJIT is free software, released under the MIT license.
-See full Copyright Notice in the COPYRIGHT file or in luajit.h.
-
-Documentation for LuaJIT is available in HTML format.
-Please point your favorite browser to:
-
- doc/luajit.html
-

README.md

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+LuaJIT 2.1 - exploitation challenge
+-----------------------------------
+
+LuaJIT is a Just-In-Time (JIT) compiler for the Lua programming language.
+
+- [LuaJIT Project Homepage](https://luajit.org/)
+
+## A few resources / hints for the challenge:
+
+- See our commits to understand what has been modified
+- [Programming in Lua](https://www.lua.org/pil/contents.html)
+    > You need no more than basic language constructs. No fancy language feature. (The authors of this challenge had previously never written a single line of Lua)
+- [Just-in-time compilation (Wikipedia)](https://en.wikipedia.org/wiki/Just-in-time_compilation)
+    > Worth reading if you have never heard of Just-in-time compilation before.
+- [Introducing LuaJIT ](https://staff.fnwi.uva.nl/h.vandermeer/docs/lua/luajit/luajit_intro.html)
+    > Explains concepts but it is slightly outdated (eg. `jit.compile()` does not exist anymore)
+
+- [LuaJIT web inspector](https://luajit.me/)
+    > Compile and inspect LuaJIT bytecode / generated Assembly
+- [Online Assembler and Disassembler](https://disasm.pro/)
+    > x86_64 assembler/disassembler
+- You are in a sandbox
+    - flag is in memory
+    - seccomp syscall filter prevents you from just running `os.execute("/bin/get_flag")` 
+    - anyway, we deleted almost every global variable
+
+- Heavy workload is required to trigger JIT compilation.
+
+This code will not be JIT-compiled:
+```lua
+f = function()
+  for i=0, 10, 1 do
+    end
+end
+f()
+```
+But this code will (notice loop boundaries):
+```lua
+f = function()
+  for i=0, 100, 1 do
+    end
+end
+f()
+```