linux-kernel - Re: [PATCH v4 1/2] x86/speculation: apply IBPB more strictly to avoid cross-process data leak

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Date:   Fri, 7 Sep 2018 08:39:08 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        "Schaufler, Casey" <casey.schaufler@...el.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v4 1/2] x86/speculation: apply IBPB more strictly to
 avoid cross-process data leak

On Thu, Sep 06, 2018 at 10:32:38AM +0200, Jiri Kosina wrote:
> From: Jiri Kosina <jkosina@...e.cz>
> 
> Currently, we are issuing IBPB only in cases when switching into a non-dumpable
> process, the rationale being to protect such 'important and security sensitive'
> processess (such as GPG) from data leak into a different userspace process via
> spectre v2.
> 
> This is however completely insufficient to provide proper userspace-to-userpace
> spectrev2 protection, as any process can poison branch buffers before being
> scheduled out, and the newly scheduled process immediately becomes spectrev2

"becomes a"

> victim.
> 
> In order to minimize the performance impact (for usecases that do require
> spectrev2 protection), issue the barrier only in cases when switching between
> processess where the victim can't be ptraced by the potential attacker (as in

"processes"

> such cases, the attacker doesn't have to bother with branch buffers at all).
> 
> Fixes: 18bf3c3ea8 ("x86/speculation: Use Indirect Branch Prediction Barrier in context switch")
> Originally-by: Tim Chen <tim.c.chen@...ux.intel.com>
> Signed-off-by: Jiri Kosina <jkosina@...e.cz>

Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh