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What is a Custom Lua Virtual Machine?

simple_x

milktea

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I've heard about the concept of a CLVM, I'm wondering...
How would one achieve such execution method?
What can be used to achieve it?
What is used in order to achieve script execution?
I know it's unstable, I want to experiment with some new execution method.

If you can write a CLVM, bare with me and teach me how it's done,

..or provide resources to learn from.
Thank you!

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DeepPain

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a custom lua vm is actually quite a stable way of execution as its what synapse uses.

basically a clvm interprets lua bytecode, it goes through each intruction one by one and performs them, for example if my script looked like this:

print(nil) --for some weird reason???

the first intruction would be OP_GETGLOBAL and then it would point to a location in the string table and for our script that would mean what it points back to is "print" then it would have OP_LOADNIL, and then finally it would have the 3rd instruction be OP_CALL.

to put it into simple terms you basically just re-create roblox's vm in your exploit

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simple_x

milktea

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@DeepPain i've heard about synapse's hook based vm
can you provide with resources to grasp the idea of recreating roblox virtual machine?

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DeepPain

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@simple_x https://github.com/the0d3v/LoukaPDF/blob/master/OVM.pdf

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simple_x

milktea

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@DeepPain thanks.
by any chance is the OVM source still somewhat relevant to nowadays standards?
if not then is HSVM source still relevant? I want to take a look at how the code is written

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Added

@Astronemi i think synapse still runs on CLVM with their own hook-based vm
bytecode is cool and all but imagine clvm :flushed:

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DeepPain

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@simple_x

i think they should be relevant just without some of the opcodes that roblox added in luau

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@_realnickk

you were right on loadk but why make a custom stack and custom bytecode format if the regular lua bytecode works fine? unless you're going to do something like syn.secure but that would only require a custom bytecode format, you were also close on the lbi

lbi's work by having a lua-coded lua vm interpret the bytecode

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@simple_x

: https://github.com/Virtual-M/OVM2, I am pretty sure its similer to CLVM, btw this is made by rain.

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is this hard to maintain like stable and not crashing?

 

just askin cuz it sounds cool especially when synapse uses it

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simple_x

milktea

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@MaximusExploit from what i've seen, it's kinda hard to maintain because if the vm changes, your exploit will break

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DeepPain

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@simple_x wha-? that doesnt make sense, if ROBLOX'S VM changes you only need to change the instructions that they changed

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simple_x

milktea

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@ghandy thanks i'll definitely check those out

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