chore(ctb): More proof-validation tests for `MIPS.sol` (#10726)

Adds a test for a separate proof validity case, where the proofs
provided are correct relative to the state witness' merkle root, but
correspond to a separate leaf that does not contain the desired program
counter address or memory address read by the instruction.

packages/contracts-bedrock/scripts/go-ffi/differential-testing.go

@@ -380,6 +380,39 @@ func DiffTestUtils() {
 		}
 		insnProof = mem.MerkleProof(uint32(pc))
 
+		output := struct {
+			MemRoot common.Hash
+			Proof   []byte
+		}{
+			MemRoot: mem.MerkleRoot(),
+			Proof:   append(insnProof[:], memProof[:]...),
+		}
+		packed, err := cannonMemoryProofArgs.Pack(&output)
+		checkErr(err, "Error encoding output")
+		fmt.Print(hexutil.Encode(packed[32:]))
+	case "cannonMemoryProofWrongLeaf":
+		// <pc, insn, memAddr, memValue>
+		mem := mipsevm.NewMemory()
+		if len(args) != 5 {
+			panic("Error: cannonMemoryProofWrongLeaf requires 4 arguments")
+		}
+		pc, err := strconv.ParseUint(args[1], 10, 32)
+		checkErr(err, "Error decocding addr")
+		insn, err := strconv.ParseUint(args[2], 10, 32)
+		checkErr(err, "Error decocding insn")
+		mem.SetMemory(uint32(pc), uint32(insn))
+
+		var insnProof, memProof [896]byte
+		memAddr, err := strconv.ParseUint(args[3], 10, 32)
+		checkErr(err, "Error decocding memAddr")
+		memValue, err := strconv.ParseUint(args[4], 10, 32)
+		checkErr(err, "Error decocding memValue")
+		mem.SetMemory(uint32(memAddr), uint32(memValue))
+
+		// Compute a valid proof for the root, but for the wrong leaves.
+		memProof = mem.MerkleProof(uint32(memAddr + 32))
+		insnProof = mem.MerkleProof(uint32(pc + 32))
+
 		output := struct {
 			MemRoot common.Hash
 			Proof   []byte

packages/contracts-bedrock/test/cannon/MIPS.t.sol

@@ -1531,6 +1531,25 @@ contract MIPS_Test is CommonTest {
         mips.step(encodeState(state), proof, 0);
     }
 
+    function test_invalid_root_different_leaf_fails() external {
+        uint32 insn = 0x0000000c; // syscall
+
+        // Initialize the state, though for the proof, use valid proofs for the instruction
+        // and the memory address, but for a different leaf that does not contain the
+        // instruction @ pc nor the memory address being read.
+        uint32 pc = 0;
+        MIPS.State memory state;
+        bytes memory proof;
+        (state.memRoot, proof) = ffi.getCannonMemoryProofWrongLeaf(pc, insn, 0x4, 0);
+        state.pc = pc;
+        state.nextPC = pc + 4;
+        state.registers[2] = 4246; // exit_group syscall
+        state.registers[4] = 0x5; // a0
+
+        vm.expectRevert(hex"000000000000000000000000000000000000000000000000000000000badf00d");
+        mips.step(encodeState(state), proof, 0);
+    }
+
     function test_jump_inDelaySlot_fails() external {
         uint16 label = 0x2;
         uint32 insn = uint32(0x08_00_00_00) | label; // j label

packages/contracts-bedrock/test/setup/FFIInterface.sol

@@ -245,6 +245,28 @@ contract FFIInterface {
         return (memRoot, proof);
     }
 
+    function getCannonMemoryProofWrongLeaf(
+        uint32 pc,
+        uint32 insn,
+        uint32 memAddr,
+        uint32 memVal
+    )
+        external
+        returns (bytes32, bytes memory)
+    {
+        string[] memory cmds = new string[](7);
+        cmds[0] = "scripts/go-ffi/go-ffi";
+        cmds[1] = "diff";
+        cmds[2] = "cannonMemoryProofWrongLeaf";
+        cmds[3] = vm.toString(pc);
+        cmds[4] = vm.toString(insn);
+        cmds[5] = vm.toString(memAddr);
+        cmds[6] = vm.toString(memVal);
+        bytes memory result = Process.run(cmds);
+        (bytes32 memRoot, bytes memory proof) = abi.decode(result, (bytes32, bytes));
+        return (memRoot, proof);
+    }
+
     function encodeScalarEcotone(uint32 _basefeeScalar, uint32 _blobbasefeeScalar) external returns (bytes32) {
         string[] memory cmds = new string[](5);
         cmds[0] = "scripts/go-ffi/go-ffi";