• Yokemate of Keyboards
    Yokemate of Keyboards
    Posts: 10062 from 2003/5/22
    From: Germany
    > you already addressed that, huh?

    It was minator who did back then :-)

    > what DOESN'T have branch prediction?

    Confusingly, Spectre seems to be more complicated than that as I just read. For instance, both Cortex-A8 and Cortex-A53 are in-order and do branch prediction, but Cortex-A53 is not vulnerable according to Arm Holdings (as linked by polluks) whereas Cortex-A8 is. So it seems to depend on how the branch predictor works specifically.

    There's a recent discussion: https://forum.level1techs.com/t/list-of-cpus-most-likely-immune-to-spectre/123128

    And this:

    "POWER9 is being patched and will not be vulnerable at ship, and there will be no performance loss versus current #POWER9 samples. Patches coming soon."

    "only the DD2.2 silicon changes were needed. DD2.2 silicon is able to close off these security holes, with the exception of the Spectre same-process read vulnerability that affects the entire CPU industry, with only changes to firmware and a small kernel change."

    Edit: As Eben Upton explains, there can be branch prediction without speculative execution. This is where I was confused, thinking the former would require the latter. It's the other way round: speculative execution can only happen after branch prediction has taken place. So as I wrote in my initial comment, vulnerable CPUs are those that do speculative execution. Branch prediction alone doesn't suffice.

    [ Edited by Andreas_Wolf 21.03.2018 - 22:16 ]
  • »05.01.18 - 22:11