linux-kernel - Re: [Patch v5 12/16] x86/speculation: Create PRCTL interface to restrict indirect branch speculation

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Date:   Sat, 17 Nov 2018 10:53:35 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Casey Schaufler <casey.schaufler@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jon Masters <jcm@...hat.com>,
        Waiman Long <longman9394@...il.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [Patch v5 12/16] x86/speculation: Create PRCTL interface to
 restrict indirect branch speculation

On Fri, 16 Nov 2018, Tim Chen wrote:

> Create PRCTL interface to restrict an application's indirect branch
> speculation.  This will protect the application against spectre v2 attack
> from another application.
> 
> Invocations:
> Check indirect branch speculation status with
> - prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, 0, 0, 0);
> 
> Enable indirect branch speculation with
> - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0);
> 
> Disable indirect branch speculation with
> - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_DISABLE, 0, 0);
> 
> Force disable indirect branch speculation with
> - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0);
> 
> See Documentation/userspace-api/spec_ctrl.rst.

I think that the fact that this talks about "indirect branch predictions" 
in general terms, but really controls only the SMT aspect of it (STIBP), 
as quite confusing.

So I believe it should either be renamed, or actually control semantics of 
IBPB as well, no?

Thanks,

-- 
Jiri Kosina
SUSE Labs