I also think they’ve shortchanged the bootstrap build mitigation. They write:

    A utility such as strip sustains the attack whenever a tampered instance participates in the rebuild, even after the compiler seed shrinks to a few hundred bytes. 

Well, yes, if you presuppose your modified binary is used, then you will find that your attack continues, but that’s only because “P iff P” is a logical tautology. It would be true even when the seed shrinks to 0 bytes, or shrinks to a negative number of bytes, or shrinks into a miniature poodle and tap-dances across your keyboard.

The question that should have been addressed is “does the tampered instance participate in the build?”, and the whole point of these minimal-byte “seed” bootstraps is that they are just enough bytes of executable to do everything else from the source. So, no, the tampered instance won’t be participating in the build. We might even deploy our own tautology and say that if a pre-existing tainted binary participates in a build, then that build was not a bootstrap build, and therefore all bootstrap builds are in fact perfectly and definitionally immune to the attack.

Honestly, this whole paper kinda reads like an academic version of a slop CVE.