These verses criticize Christian faith, but does Allah promise in the Quran or anywhere else eternal salvation?
Allah promises eternal damnation for attributing divinity to Jesus (pbuh).
There's also eternal damnation for rejecting Islam as Allah sent this latest religion to all mankind thus abrogating previous dispensations
And yes, Allah promises eternal salvation for those who convert to Islam:
098.001 Those who disbelieve among the People of the Scripture and the idolaters could not have left off (erring) till the clear proof came unto them,
098.002 A messenger from Allah, reading purified pages
098.003 Containing correct scriptures.
098.004 Nor were the People of the Scripture divided until after the clear proof came unto them.
098.005 And they are ordered naught else than to serve Allah, keeping religion pure for Him, as men by nature upright, and to establish worship and to pay the poor-due. That is true religion.
098.006 Lo! those who disbelieve, among the People of the Scripture and the idolaters, will abide in fire of hell. They are the worst of created beings.
098.007 (And) lo! those who believe and do good works are the best of created beings.
098.008 Their reward is with their Lord: Gardens of Eden underneath which rivers flow, wherein they dwell for ever. Allah hath pleasure in them and they have pleasure in Him. This is (in store) for him who feareth his Lord.
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007.157 Those who follow the messenger, the Prophet who can neither read nor write, whom they will find described in the Torah and the Gospel (which are) with them. He will enjoin on them that which is right and forbid them that which is wrong. He will make lawful for them all good things and prohibit for them only the foul; and he will relieve them of their burden and the fetters that they used to wear. Then those who believe in him, and honour him, and help him, and follow the light which is sent down with him: they are the successful.
007.158 Say (O Muhammad): O mankind! Lo! I am the messenger of Allah to you all - (the messenger of) Him unto Whom belongeth the Sovereignty of the heavens and the earth. There is no God save Him. He quickeneth and He giveth death. So believe in Allah and His messenger, the Prophet who can neither read nor write, who believeth in Allah and in His Words, and follow him that haply ye may be led aright.