On Tue, 2018-01-23 at 17:00 -0800, Andy Lutomirski wrote: > On Tue, Jan 23, 2018 at 4:47 PM, Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> wrote: > > > > On 01/23/2018 03:14 PM, Woodhouse, David wrote: > > > > > > On Tue, 2018-01-23 at 14:49 -0800, Andi Kleen wrote: > > > > > > > > > > > > > > Not sure. Maybe to start, the answer might be to allow it to be set for > > > > > the ultra-paranoid, but in general don't enable it by default. Having it > > > > > enabled would be an alternative to someone deciding to disable SMT, since > > > > > that would have even more of a performance impact. > > > > I agree. A reasonable strategy would be to only enable it for > > > > processes that have dumpable disabled. This should be already set for > > > > high value processes like GPG, and allows others to opt-in if > > > > they need to. > > > That seems to make sense, and I think was the solution we were > > > approaching for IBPB on context switch too, right? > > > > > > Are we generally agreed on dumpable as the criterion for both of those? > > > > > It is a reasonable approach. Let a process who needs max security > > opt in with disabled dumpable. It can have a flush with IBPB clear before > > starting to run, and have STIBP set while running. > > > Do we maybe want a separate opt in? I can easily imagine things like > web browsers that *don't* want to be non-dumpable but do want this > opt-in. This is to protect you from another local process running on a HT sibling. Not the kind of thing that web browsers are normally worrying about. > Also, what's the performance hit of STIBP? Varies per CPU generation, but generally approaching that of full IBRS I think? I don't recall looking at this specifically (since we haven't actually used it for this yet).
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