Re: [PATCH v2 2/3] x86/speculation: Apply IBPB more strictly to avoid cross-process spectre v2 leak

[Jiri Kosina]

On Mon, 3 Sep 2018, Peter Zijlstra wrote:

> >  		if (tsk && tsk->mm &&
> >  		    tsk->mm->context.ctx_id != last_ctx_id &&
> > -		    get_dumpable(tsk->mm) != SUID_DUMP_USER)
> > +		    ___ptrace_may_access(tsk, current, PTRACE_MODE_IBPB))
> >  			indirect_branch_prediction_barrier();
> 
> So the question posed here is: can @next ptrace @prev?
> 
> Which confuses me greatly; it is @prev doing the BTB poisoning for
> @next, so we want to know if @prev can ptrace @next, no?

Good catch, it's the other way around, thanks.

I'll wait for more review and send eventually v3 properly threaded (sorry 
for that as well ... not the best monday I've had today).

-- 
Jiri Kosina
SUSE Labs