I tried reading and gave up at the "Headline"...

Quoting from the bug analysis:

>Headline. The crash is real and reproducible. With musl instrumentation we pin the in-process mechanism precisely: a thread's own store to a freshly- faulted anonymous page becomes invisible to that same thread's reload ~10 instructions later, because the page's backing is replaced mid-function. A pagemap read at the instant of the fault shows the backing is the kernel's zero page. A captured core dump confirms the crash site with matched virtual addresses. The mechanism localizes to the interaction between the per-VMA-lock anonymous-fault fast path and a concurrent munmap's TLB shootdown. A source-level review of Linux 7.0.12 identifies a specific race in that interaction, and a git comparison across v6.19/v7.0/v7.1/mainline identifies the v7.0-introduced change on the munmap-teardown side that widens it.

"a thread's own store to a freshly- faulted anonymous page becomes invisible to that same thread's reload ~10 instructions later, because the page's backing is replaced mid-function." -> ??? What's a "backing" of a page? Freshly-faulted? Fresh fries? "~10 instructions later"?

"A pagemap read at the instant of the fault shows the backing is the kernel's zero page." -> Backing?

"The mechanism localizes to the interaction between the per-VMA-lock anonymous-fault fast path and a concurrent munmap's TLB shootdown." -> How can a mechanism "localize"?

And more.

This is... words strung together. Nothing more. I wonder how people read and make sense of this.

In case people have forgotten what real technical writing looks like, here's a sample (I am not the author): https://yifan.lu/2019/01/11/the-first-f00d-exploit/

    The overflow would still overflow; the use-after-free would still use after free; a musl mask race would still race. 

Reading an AI-generated bug report is awful.

Nice sleuthing, nonsense explanation. An extra TLB flush is never an error. (The CPU is free to flush whenever it feels like doing so.) The error seems to be that somehow a zero-page PTE was present when it shouldn’t have been.

This sounds to me like either (a) a complex race involving a CPU migration at an awkward time or (b) a bug in the zap path transiently exposing wrong PTEs.

Also, I don’t think the zero page has pfn zero.

If I had to throw a dart, I would guess that direct page table zapping is allowing a CPU to read through a higher-level-paging-structure cached entry to a table that has been freed and reused. Yuck. I’ve debugged one of these before.

soulless unreadable AI slop