Anon4 (No.delete@this.example.com) on July 14, 2022 5:05 pm wrote:
> anon2 (anon.delete@this.anon.com) on July 14, 2022 4:29 pm wrote:
> > No it wasn't, it was BTB poisoning to influence indirect branches.
> > Branch direction forwards or backwads is not relevant.
>
> I've had my head to much on CFI recently.... forward edge, obviously branch direction is not relevant.
>
> > Some CPUs use BTB for return branches in some situations. This is not somehow new nor was unknown at the
> > time. It was explicitly called out in a public discussion about the fix several years ago, actually.
>
> And was thought not to be exploitable, some people thought it was exploitable
> however they could not come up with a practical attack at the time.
>

According to my definition of "practical" Spectre-v2 never was practical attack vector, with
or without retpoline mitigation.
Ergo, retpolines were and are wastage of everybody's money and energy.

> Given the mitigation cost no one was going to roll out an expensive speculative (sic) mitigation against
> an attack which was not thought to be practical at the time. That 'expensive' is in money, performance
> losses cost real money for the hyperscalers and major ones can make a service economically unviable.
>