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 13:00:40 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     "Schaufler, Casey" <casey.schaufler@...el.com>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        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 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?

Thanks,

-- 
Jiri Kosina
SUSE Labs