I went to smith Dawnbreaker and I could only put it up to flawless. I have 100 in smithing, and perked fully up the right side of the tree to daedric. It takes an ebony ingot, so what is the deal? How do I get it up to legendary? Flawless just won't do on master.

+smithing enchanted gear: easy to find in vendors and break down, can be put on ring, neclace, gloves, and chest.

+smithing potions: blistwort and glowing mushrooms are two common ingredients to make the potions.

EDIT: Glad to hear your having a difficult time on master difficulty, must be bacause you didnt exploit the above mentioned tips. . .good for you and im glad you enjoy skyrim

try drinking any potion that improve smithing skill.i dont remember wether i ever tried that to smith the lovely blade up to legendary, but it should do.. i guess..

Yeah, keep eyes open for the +smithing gear at vendors (or rarely, drops)- usually gauntlets, rings and necklaces. Highest you can get on an item is peerless, +25%. Blacksmithing potions- can occasionally get from drops, but try pickpocketing the various blacksmiths around Skyrim, and burgling thier homes and shops. There are a number of potions you can steal that way. Also, what level was your char when you got the Dawnbreaker? Makes a huge difference in how high of a damage you can get out of it through improvements.

nevermind, turns out i was wrong.

Actually dawn breaker isnt lvled so it doesn't matter the lvl u got it.
Also highest u can get is legendary, the reason u can't get this is that the perk for ebony smithing doesn't affect this.( no perks do ). Also the highest blacksmithing potion u can get is +50% and it is the blacksmith elixir

unless you have alchemy at 100, the right perks, and fortify alchemy gear on, then 120% is easy to obtain.

Edit: also you are correct, dawnbreaker has set stats not dependent on level it seems

You need 168 in Smithing to make it legendary. There's several tiers of legendary though - if you improve an ebony sword (or any other base weapon which you have perked) with 168 blacksmithing, it'll be more powerful than if you do it with "just" 100.

Enchant:
1.A blacksmith's apron
2.Gloves
3.Ring
4.Tiara

With fortify smithing 25% (depending on your enchanting level)
Potions also help, but the more percentage stacked when making the weapon, the better it'll be.