No, you could also find a gadget with ROP techniques. The eBPF thing in the paper was purely due to convenience of exploitation.

I think that's almost but not quite exactly right.

Spectre variant 2 attacks vulnerable indirect jump code patterns that exist in the kernel (or some other process), but doesn't require running the attacker's code.

Spectre variant 1 allows you to infer the contents of memory in the same address space, so that's the one where you'd use eBPF to attack the kernel.

Meltdown (variant 3) if I understand correctly can infer memory contents of other address spaces without relying on any assumptions about the code running in the other address space.

https://security.googleblog.com/2018/01/more-details-about-m...

> That link no longer loads for me.

Oh, right, ycombinator's URL parser is broken. I fixed the link to work around the buggy parser....