[$] Injecting speculation barriers into BPF programs

The disclosure of the Spectre
class of hardware vulnerabilities created a lot of pain for kernel
developers (and many others). That pain was especially acutely felt in the
BPF community. While an attacker might have to painfully search the kernel
code base for exploitable code, an attacker using BPF can simply write and
load their own speculation gadgets, which is a much more efficient way of
operating. The BPF community reacted by, among other things, disallowing
the loading of programs that may include speculation gadgets. Luis
Gerhorst would like to change that situation with this patch
series that takes a more direct approach to the problem.