Disable "Moved wrongly" check via coremod

[Rsge]

Hi.

I am trying to write a small coremod for my 1.12.2 private server to disable the "Moved wrongly" and maybe the "Moved too quickly" checks in NetHandlerPlayServer, as it is very buggy with Psi's Blink-spell, just teleports you back constantly.

 

First of all, I know this is a security risk because of hacking, but as I said, it's a private server so I don't care about that.

Second, I sadly don't have much experience in modding Minecraft and especially not in bytecode and that sort of stuff in Java.

 

So I got most of the code from this post and just tried to update it for 1.12.2.

But according to the printlns I added in analyzeClass the methods I need to patch (processVehicleMove and processPlayer) aren't even scanned through.

So I don't know if I'm doing the scanning wrong or if there is something else.

Everything else seems to work, the mod is loaded and is shown in the Mods-section as expected, so the error must be in this class.

 

Any help would be appreciated.

Thanks : )

 

package rsge.mods.blinkfixer.asm;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.tree.AbstractInsnNode;
import org.objectweb.asm.tree.ClassNode;
import org.objectweb.asm.tree.InsnList;
import org.objectweb.asm.tree.JumpInsnNode;
import org.objectweb.asm.tree.LabelNode;
import org.objectweb.asm.tree.LdcInsnNode;
import org.objectweb.asm.tree.MethodNode;

import net.minecraft.launchwrapper.IClassTransformer;


/**
 * Removes the "Moved Wrongly" checks from {@link net.minecraft.network.NetHandlerPlayServer}
 * 
 * @author Rsge
 */
public class NetHandlerPlayServerTransformer implements IClassTransformer
{
	private static enum MovedWronglyState
	{
		FIND_LDC, FIND_DCMPL, FIND_IFLE, DONE
	}

	/**
	 * Before: LDC2_W 0.0625 DCMPL IFLE <label> (code to execute if the value was greater) After: LDC2_W 0.0625 DCMPL IFLE <label> GOTO <same label> (code that
	 * no longer ever gets executed) I leave the IFLE in just so the DCMPL result gets popped off the stack
	 */
	private boolean disableMovedWrongly(MethodNode node)
	{
		MovedWronglyState state = MovedWronglyState.FIND_LDC;
		InsnList insnList = node.instructions;
		AbstractInsnNode insn = insnList.getFirst();
		AbstractInsnNode patchTarget = null;
		LabelNode gotoLabel = null;

		while (insn != null && state != MovedWronglyState.DONE)
		{
			switch (state)
			{
			case FIND_LDC:
				if (insn.getOpcode() == Opcodes.LDC)
				{
					Object value = ((LdcInsnNode) insn).cst;
					// 0.0625 is 1/16, which can be perfectly represented by a float (power of two denominator)
					if (value instanceof Double && ((Double) value).doubleValue() == 0.0625)
					{
						state = MovedWronglyState.FIND_DCMPL;
					}

				}
				break;

			case FIND_DCMPL:
				if (insn.getOpcode() == Opcodes.DCMPL)
				{
					state = MovedWronglyState.FIND_IFLE;
				}
				else
				{
					state = MovedWronglyState.FIND_LDC;
				}
				break;

			case FIND_IFLE:
				if (insn.getOpcode() == Opcodes.IFLE)
				{
					state = MovedWronglyState.DONE;
					gotoLabel = ((JumpInsnNode) insn).label;
					patchTarget = insn;
				}
				else
				{
					state = MovedWronglyState.FIND_LDC;
				}
				break;
			case DONE:
				break;
			default:
				break;
			}
			insn = insn.getNext();
		}

		if (state == MovedWronglyState.DONE)
		{
			applyGotoPatch(insnList, gotoLabel, patchTarget);
			return true;
		}
		else
		{
			return false;
		}

	}

	/* ————————————————————————————————————————————————————— */

	private static enum MovedTooQuicklyState
	{
		FIND_LDC, FIND_DCMPL, FIND_IFLE, DONE
	}

	/**
	 * Before: LDC2_W 100.0 DCMPL IFLE <label> (code to execute if the value was greater) After: LDC2_W 100.0 DCMPL IFLE <label> GOTO <same label> (code that no
	 * longer ever gets executed) As above, I leave the IFLE in so the DCMPL result gets popped off the stack
	 */
	private boolean disableMovedTooQuickly(MethodNode node)
	{
		MovedTooQuicklyState state = MovedTooQuicklyState.FIND_LDC;
		InsnList insnList = node.instructions;
		AbstractInsnNode insn = insnList.getFirst();
		AbstractInsnNode patchTarget = null;
		LabelNode gotoLabel = null;

		while (insn != null && state != MovedTooQuicklyState.DONE)
		{
			switch (state)
			{
			case FIND_LDC:
				if (insn.getOpcode() == Opcodes.LDC)
				{
					Object value = ((LdcInsnNode) insn).cst;
					if (value instanceof Double && ((Double) value).doubleValue() == 100.0)
					{
						state = MovedTooQuicklyState.FIND_DCMPL;
					}
				}
				break;

			case FIND_DCMPL:
				if (insn.getOpcode() == Opcodes.DCMPL)
				{
					state = MovedTooQuicklyState.FIND_IFLE;
				}
				else
				{
					state = MovedTooQuicklyState.FIND_LDC;
				}
				break;

			case FIND_IFLE:
				if (insn.getOpcode() == Opcodes.IFLE)
				{
					state = MovedTooQuicklyState.DONE;
					gotoLabel = ((JumpInsnNode) insn).label;
					patchTarget = insn;
				}
				else
				{
					state = MovedTooQuicklyState.FIND_LDC;
				}
				break;
			case DONE:
				break;
			default:
				break;
			}

			insn = insn.getNext();
		}

		if (state == MovedTooQuicklyState.DONE)
		{
			applyGotoPatch(insnList, gotoLabel, patchTarget);
			return true;
		}
		else
		{
			return false;
		}

	}

	/* ————————————————————————————————————————————————————— */

	private void applyGotoPatch(InsnList instr, LabelNode lbl, AbstractInsnNode trg)
	{
		instr.insert(trg, generatePatch(lbl));
	}

	private InsnList generatePatch(LabelNode lbl)
	{
		InsnList list = new InsnList();
		list.add(new JumpInsnNode(Opcodes.GOTO, lbl));
		return list;
	}

	/* ————————————————————————————————————————————————————— */

	private boolean analyzeClass(ClassNode node)
	{
		boolean successVehicleMove = false;
		boolean successProcessPlayer = false;

		for (MethodNode method : node.methods)
		{
			System.out.println("Method: " + method.name);
			// Method processVehicleMove
			if (method.name.equals("a") && method.desc.equals("(Lll;)V"))
			{
				successVehicleMove = disableMovedTooQuickly(method) && disableMovedWrongly(method);
			}
			// Method processPlayer
			if (method.name.equals("a") && method.desc.equals("(Llk;)V"))
			{
				successProcessPlayer = disableMovedTooQuickly(method) && disableMovedWrongly(method);
			}
		}
		if (!(successVehicleMove && successProcessPlayer))
			System.out.println("Unabled to find method to patch");
		
		return successVehicleMove && successProcessPlayer;
	}

	@Override
	public byte[] transform(String name, String transname, byte[] bytes)
	{
		if (transname.contains("net.minecraft.network"))
			System.out.println(name + "; " + transname);
		if (transname.contains("net.minecraft.network.NetHandlerPlayServer"))
		{
			System.out.println("Class to transform: " + transname);
			ClassReader reader = new ClassReader(bytes);
			ClassNode node = new ClassNode();
			reader.accept(node, 0);

			if (analyzeClass(node))
			{
				ClassWriter writer = new ClassWriter(ClassWriter.COMPUTE_MAXS | ClassWriter.COMPUTE_FRAMES);
				node.accept(writer);
				bytes = writer.toByteArray();
			}
			else
			{
				System.out.println("Failed to patch methods");
			}
		}
		return bytes;
	}
}

 

Edited July 8, 2019 by Rsge

[Cadiboo]

Thats not going to work, thats extremely old code targeted at a very old version. If you don't already know how to write a coremod, don't. You need to have extensive knowledge of ASM, IJVM code and how the JVM works to write a coremod.

 

9 hours ago, Rsge said:

as it is very buggy with Psi's Blink-spell

Tell the author to fix this issue then.

[Rsge]

6 hours ago, Cadiboo said:

thats extremely old code targeted at a very old version.

That's why I'm trying to update it so it does work.

 

6 hours ago, Cadiboo said:

Tell the author to fix this issue then. 

I don't think Vazkii will disable these checks as they have their security reasons.

Also, it seems to be different on different servers/modpacks, as another 1.12.2-modpack I played didn't have this issue - at least not as bad as in the other pack.

So I don't think this is necessarily a bug in Psi itself... - I'll report it regardless, if he still does 1.12.2-fixes...

Edited July 9, 2019 by Rsge