Messages in this thread | | | Subject | Re: x86/retpoline: Fill RSB on context switch for affected CPUs | From | "Maciej S. Szmigiero" <> | Date | Fri, 9 Mar 2018 16:33:51 +0100 |
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On 09.03.2018 16:14, Andi Kleen wrote: >> Shouldn't the RSB filling on context switch also be done on non-IBPB >> CPUs to protect (retpolined) user space tasks from other user space >> tasks? > > The comment is actually incorrect. There's no risk to hit user space > addresses if we have KPTI and NX (which is fairly universal). > > It's mainly needed on Skylake era CPUs. > > Should fix the comment. I'll send a patch.
But what about userspace-to-userspace attacks? - the ones that IBPB on context switches currently protects against (at least for high-value, or as implemented currently, non-dumpable, processes)?
If understand the issue correctly, high-value user space processes can be protected from other user space processes even on CPUs that lack IBPB as long as they are recompiled with retpolines and there is no danger of RSB entries from one process being used by another one after a context switch. For Skyklake this would not be enough, but there we'll (hopefully) have the IBPB instead.
> -Andi >
Maciej
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