Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app protection modes

[Thomas Gleixner]

On Mon, 19 Nov 2018, Jiri Kosina wrote:
> On Mon, 19 Nov 2018, Thomas Gleixner wrote:
> 
> > > On Sat, 17 Nov 2018, Jiri Kosina wrote:
> > 
> > > Subject: [PATCH] x86/speculation: enforce STIBP for SECCOMP tasks in lite mode
> > > 
> > > If 'lite' mode of app2app protection from spectre_v2 is selected on
> > > kernel command-line, we are currently applying STIBP protection to
> > > non-dumpable tasks, and tasks that have explicitly requested such
> > > protection via
> > > 
> > > 	prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0);
> > > 
> > > Let's extend this to cover also SECCOMP tasks (analogically to how we
> > > apply SSBD protection).
> > 
> > Right. And SSBD does not fiddle with dumpable.
> > 
> > Willy had concerns about the (ab)use of dumpable so I'm holding off on that
> > bit for now.
> 
> Yeah. IBPB implementation used to check the dumpability of tasks during 
> rescheduling, but that went away later.
> 
> I still think that ideally that 'app2app' setting would toggle how IBPB is 
> being used as well, something along the lines:
> 
> lite:
> 	- STIBP for the ones marked via prctl() and SECCOMP with the TIF_ 
> 	  flag
> 	- ibpb_needed() returning true for the same
> 
> strict:
> 	- STIBP: as currently implemented
> 	- ibpb_needed() returning always true
> 
> off:
> 	- neither STIBP nor IBPB applied ever
> 
> That's give us also some % of performance lost via IBPB back.
> 
> Makes sense?

Except for the naming convention, yes. See other mail.

Thanks,

	tglx