 function step(bytes calldata _stateData, bytes calldata _proof, bytes32 _localContext) public returns (bytes32) {
        unchecked {
...
 uint32 val = execute(insn, rs, rt, mem) & 0xffFFffFF; // swr outputs more than 4 bytes without the mask
...
     // write memory
            if (storeAddr != 0xFF_FF_FF_FF) {
                writeMem(storeAddr, 1, val);
            }

            // write back the value to destination register
            return handleRd(rdReg, val, true);
        }
}
function execute(uint32 insn, uint32 rs, uint32 rt, uint32 mem) internal pure returns (uint32 out) {
        unchecked {
...
if (opcode == 0 || (opcode >= 8 && opcode < 0xF)) {
...
} else {
                
                if (opcode == 0x1C) {
                    uint32 func = insn & 0x3f; // 6-bits
                    // mul
                    if (func == 0x2) {
>>>                        return uint32(int32(rs) * int32(rt)); 
                    }
                    // clz, clo
                    else if (func == 0x20 || func == 0x21) {
                    ... } 
                 ...}
    ...
    }
...
}
+++  import "@openzeppelin/contracts/utils/math/SafeMath.sol";

function execute(uint32 insn, uint32 rs, uint32 rt, uint32 mem) internal pure returns (uint32 out) {
    ...
    if (opcode == 0x1C) {
        uint32 func = insn & 0x3f; // 6-bits
        // mul
        if (func == 0x2) {
---            return uint32(int32(rs) * int32(rt));
+++            int64 result = int64(int32(rs)) * int64(int32(rt));
+++            require(result <= int32.max && result >= int32.min, "Multiplication overflow");
+++            return uint32(int32(result));
        }
        // clz, clo
        else if (func == 0x20 || func == 0x21) {
            ...
        }
    }
    ...
}
