Great question — answering as the UphillTech team:
We trust the integrity of the data retrieved from swap because the storage hardware has checksums, CRCs, and such. In one of the comments above, you say: true, but it won't protect against bit flips outside of the disk itself "It" meaning the disk's checksums here. That is true, but SATA uses 32-bit CRCs for commands and data. Thus, you have a 1 in 4 billion chance of corrupting data undetectably between the disk and the SATA controller. That means that a continuous error source could introduce an error as often as every 125 MiB transferred, but a rare, random error source like cosmic rays would cause undetectable errors at a vanishingly small rate. Realize also that if you've got a source...
Full answer by Warren Young: https://unix.stackexchange.com/a/276961 (CC BY-SA 3.0).
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