You are incorrect. According to Genesis, God created everything good. God did not create evil. To say that any evil comes from God is to deny His perfect Holiness. To understand this better we have to first understand that evil is not a creation, it is the absence of a good. God created all things good. But God gave us and the angels freewill to choose to do what is right or not to choose to do what is right. Since all things that are good come from God, any place that is devoid of God is going to also be devoid of anything good. And that kind of place is what we call Hell.
To understand why Satan is forever evil we have to understand how angels are different than us. Unlike us humans who have a physical brain which has it's limits and often can give us clouded judgment resulting in a change of mind, angels don't have a physical body and therefore have pure thought and perfect understanding. So when angels were given a choice to go with God's plan for the Incarnation or to reject it, they understood perfectly the choice they were making. That's why when satan made his decision not to follow God's plan it was a final decision that won't ever change. In other words, Satan freely chose to reject God forever.