Messages in this thread | | | Subject | Re: [PATCH] x86/speculation: Use Indirect Branch Prediction Barrier in context switch | From | Tim Chen <> | Date | Tue, 30 Jan 2018 16:25:26 -0800 |
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On 01/30/2018 02:43 PM, Borislav Petkov wrote: > On Tue, Jan 30, 2018 at 02:26:53PM -0800, Tim Chen wrote: >> If the process has multiple threads running on different cpus, > > I'm talking about issuing the barrier in set_dumpable(). What threads on > multiple CPUs? >
As dumpable is a property in mm->flags, it affects all threads running on other cpus sharing the same mm. If you issue IBPB only on the cpu that perform the set_dumpable(), the theoretical hole you are trying to close still exist on threads running on other cpu.
time -----> (cpu A) set_dumpable victim (thread1), issue IBPB (cpu B) attacker -> victim (thread2), missed IBPB -> attacker -> victim (IBPB issued)
That said, I think the risk is minuscule and is not worth the cost to set IBPB on the other cpus.
Tim
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