linux-kernel - RE: [PATCH v6 1/3] x86/speculation: apply IBPB more strictly to avoid cross-process data leak

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Date:   Fri, 14 Sep 2018 13:05:10 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jiri Kosina <jikos@...nel.org>
cc:     "Schaufler, Casey" <casey.schaufler@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCH v6 1/3] x86/speculation: apply IBPB more strictly to
 avoid cross-process data leak

On Fri, 14 Sep 2018, Jiri Kosina wrote:
> On Thu, 13 Sep 2018, Schaufler, Casey wrote:
> 
> > > -	return security_ptrace_access_check(task, mode);
> > > +	if (!(mode & PTRACE_MODE_NOACCESS_CHK))
> > > +		return security_ptrace_access_check(task, mode);
> > > +	return 0;
> > 
> > Because PTRACE_MODE_IBPB includes PTRACE_MODE_NOAUDIT you
> > shouldn't need this change. 
> 
> That is true, but that's not my concern here. 
> 
> 	security_ptrace_access_check() -> call_int_hook() -> P->hook.FUNC().
> 
> If it's somehow guaranteed that all functions called this ways are fine to 
> be called from scheduler context (wrt. locks), then it's all fine and I'll 
> happily drop that check.
> 
> Is it guaranteed?

The related question is whether it is guaranteed for backports. We don't
want to end up with a separate hell there.

Thanks,

	tglx