Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation

[Tim Chen]

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.

Tim