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Beating Google's kernelCTF PoW using AVX512
PoW is gone 🦀🦀
In May 2025, my Crusaders of Rust teammates William Liu ( FizzBuzz101) and Savy Dicanosa ( Syst3mFailure) discovered and developed an exploit of a use-after-free bug in Linux's packet scheduler. The numbers don't seem to add up: even assuming an instant exploit and form submission, the VM boot time and proof of work already take 6.5 seconds. Inspecting the assembly revealed that both GCC and clang were unrolling the loop, converting the_mm512_set1_epi64 instructions into vbroadcastsd zmm, m64 instructions—one per limb—and then running out of vector registers during regalloc.
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