I'm really amazed by the simplicity of the meltdown gadget. After the initial blog post I played with a few variants, but always got the zeroed out register in

I'm really amazed by the simplicity of the meltdown gadget. After the initial blog post I played with a few variants, but always got the zeroed out register in the speculative branch. I guess what people (including me) were looking for here was some other side channel or instruction that did not have this mitigation in place (e.g. I had hoped a cmpxchg would leak whether the target memory address matches the register to compare with). The shl/retry loop makes a lot of sense if you instead assume that the mitigation was implemented improperly and can race subsequent uops. I really can't imagine why this data ever made it to the bypass network to be available to other uops.