linux-kernel - Re: [PATCH v3 2/3] x86/speculation: apply IBPB more strictly to avoid cross-process data leak

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Message-ID: <nycvar.YFH.7.76.1809050953440.15880@cbobk.fhfr.pm>
Date:   Wed, 5 Sep 2018 09:55:35 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        Oleg Nesterov <oleg@...hat.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v3 2/3] x86/speculation: apply IBPB more strictly to
 avoid cross-process data leak

On Wed, 5 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(current, tsk, PTRACE_MODE_IBPB))
> >  			indirect_branch_prediction_barrier();
> 
> See how the new (first) argument is 'current' and you could've just used
> the old __ptrace_may_access().

Yeah, 1/3 is dropped in my current series already; this was cherry-picked 
from original Tim's series, but it is indeed superfluous.

Thanks,

-- 
Jiri Kosina
SUSE Labs