Smali Code Patching Guide

Changing the Return Value in Methods

Example: checkDebugger() Function

The original checkDebugger() function in smali checks whether a debugger is connected. By modifying this function, we can change its behavior to always return a specific result.

Original Code

.method public checkDebugger()Z
    .locals 1

    .line 30
    invoke-static {}, Landroid/os/Debug;->isDebuggerConnected()Z

    move-result v0

    return v0
.end method

In this case, the method returns the actual result of isDebuggerConnected(). To modify it, we can overwrite the value of v0 before returning it.

Modified Code

.method public checkDebugger()Z
    .locals 1

    .line 30
    invoke-static {}, Landroid/os/Debug;->isDebuggerConnected()Z

    move-result v0

    const v0, 0x0  # Overwrite the result to always be false

    return v0
.end method

Now, the method always returns false (represented by 0x0), no matter the actual result of the isDebuggerConnected() function.

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Flipping the Logic in Conditionals (IF-ELSE-GOTO Patching)

Example: Processing getHit() Method in a Game

Here, we modify a method that processes a player getting hit, depending on whether the player has a shield. By flipping the conditional logic, we can change how the game behaves.

Original Code

.method public getHit()V
    .locals 3

    .line 37
    iget-boolean v0, p0, Lcom/apphacking/smalitwo/Player;->shield:Z

    const/4 v1, 0x0
    const/4 v2, 0x1

    if-ne v0, v2, :cond_0  # If shield is not active, go to cond_0

    .line 39
    iput-boolean v1, p0, Lcom/apphacking/smalitwo/Player;->shield:Z
    goto :goto_0

    .line 42
    :cond_0
    iget v0, p0, Lcom/apphacking/smalitwo/Player;->lives:I
    sub-int/2addr v0, v2
    iput v0, p0, Lcom/apphacking/smalitwo/Player;->lives:I

    .line 44
    if-lez v0, :cond_1

    .line 46
    iput-boolean v2, p0, Lcom/apphacking/smalitwo/Player;->state:Z
    goto :goto_0

    .line 49
    :cond_1
    iput-boolean v1, p0, Lcom/apphacking/smalitwo/Player;->state:Z

    .line 52
    :goto_0
    return-void
.end method

In this code, when the player has a shield (if-ne v0, v2), they don't lose lives. To flip this logic, we can change the if-ne to if-eq so that now the player will lose lives when they have a shield.

Modified Code

.method public getHit()V
    .locals 3

    .line 37
    iget-boolean v0, p0, Lcom/apphacking/smalitwo/Player;->shield:Z

    const/4 v1, 0x0
    const/4 v2, 0x1

    if-eq v0, v2, :cond_0  # If shield is active, go to cond_0 (Flipped Logic)

    .line 39
    iput-boolean v1, p0, Lcom/apphacking/smalitwo/Player;->shield:Z
    goto :goto_0

    .line 42
    :cond_0
    iget v0, p0, Lcom/apphacking/smalitwo/Player;->lives:I
    sub-int/2addr v0, v2
    iput v0, p0, Lcom/apphacking/smalitwo/Player;->lives:I

    .line 44
    if-lez v0, :cond_1

    .line 46
    iput-boolean v2, p0, Lcom/apphacking/smalitwo/Player;->state:Z
    goto :goto_0

    .line 49
    :cond_1
    iput-boolean v1, p0, Lcom/apphacking/smalitwo/Player;->state:Z

    .line 52
    :goto_0
    return-void
.end method

Now, the game logic is reversed, and the player loses lives when they have a shield.

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Deleting Code to Alter Game Logic

In some cases, you can remove certain instructions to alter the game behavior entirely.

Example: processGame() Method in Java

public void processGame() {
    // Create new Player Object
    Player player = new Player();
    if (player.hasItem(MasterCap)) {
        player.power += 100;
    } else {
        player.power += 10;
    }
}

In smali, this code translates into conditional logic that adds power based on whether the player has the MasterCap.

Original Smali Code

.method public hasItem(Lcom/apphacking/smalitwo/Player;)V
    .locals 1
    .param p1, "player"    # Lcom/apphacking/smalitwo/Player;

    .line 15
    iget-boolean v0, p1, Lcom/apphacking/smalitwo/Player;->masterCap:Z

    if-eqz v0, :cond_0  # Check if the player does not have the MasterCap

    .line 17
    iget v0, p1, Lcom/apphacking/smalitwo/Player;->power:I
    add-int/lit8 v0, v0, 0x64  # Add 100 power
    iput v0, p1, Lcom/apphacking/smalitwo/Player;->power:I

    goto :goto_0

    .line 20
    :cond_0
    iget v0, p1, Lcom/apphacking/smalitwo/Player;->power:I
    add-int/lit8 v0, v0, 0xA   # Add 10 power
    iput v0, p1, Lcom/apphacking/smalitwo/Player;->power:I

    .line 23
    :goto_0
    return-void
.end method

By removing the if-eqz line, the game will always give the player 100 power, regardless of whether they have the MasterCap.

Modified Code

.method public hasItem(Lcom/apphacking/smalitwo/Player;)V
    .locals 1
    .param p1, "player"    # Lcom/apphacking/smalitwo/Player;

    .line 17
    iget v0, p1, Lcom/apphacking/smalitwo/Player;->power:I
    add-int/lit8 v0, v0, 0x64  # Always add 100 power
    iput v0, p1, Lcom/apphacking/smalitwo/Player;->power:I

    .line 23
    return-void
.end method

By eliminating the condition, the player now gets a 100 power boost unconditionally.

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Changing Jump Instructions

Jump instructions (goto, if-*) can be modified to change how the program flow behaves.

Example: Modifying GOTO

In the same method, we can alter the jump instruction to make the player gain 110 power instead of choosing between 100 or 10.

Original Code

goto :goto_0

Modified Code

goto :cond_0  # Redirect to give both 10 and 100 power

Now the program first adds 10 power and then immediately adds 100 power, giving a total of 110.

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Additional Method: Manipulating Currency in a Game

New Method: increaseCurrency()

This method will increase the player's in-game currency.

.method public increaseCurrency()V
    .locals 2

    .line 25
    iget v0, p0, Lcom/apphacking/smalitwo/Player;->currency:I
    const/16 v1, 0x3E8  # Add 1000 currency
    add-int/2addr v0, v1
    iput v0, p0, Lcom/apphacking/smalitwo/Player;->currency:I

    .line 

28
    return-void
.end method

Now the player will receive 1000 in-game currency every time this method is called.