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    SubjectRE: [PATCH 0/7] IBRS patch series
    > On Thu, Jan 4, 2018 at 11:19 AM, David Woodhouse <>
    > wrote:
    > >
    > > On Skylake the target for a 'ret' instruction may also come from the
    > > BTB. So if you ever let the RSB (which remembers where the 'call's came
    > > from get empty, you end up vulnerable.
    > That sounds like it could cause mispredicts, but it doesn't sound _exploitable_.
    > Sure, interrupts in between the call instruction and the 'ret' could
    > overflow the return stack. And we could migrate to another CPU. And so
    > apparently SMM clears the return stack too.
    > ... but again, none of them sound even remotely _exploitable_.

    this is about a level of paranoia you are comfortable with.

    Retpoline on Skylake raises the bar for the issue enormously, but there are a set of corner cases that exist and that are not trivial to prove you dealt with them.

    personally I am comfortable with retpoline on Skylake, but I would like to have IBRS as an opt in for the paranoid.

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