linux-kernel - Re: [PATCH RESEND] x86/speculation: Fix user-mode spectre-v2 protection with KERNEL

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Message-ID: <20230220175929.2laflfb2met6y3kc@treble>
Date:   Mon, 20 Feb 2023 09:59:29 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     KP Singh <kpsingh@...nel.org>, linux-kernel@...r.kernel.org,
        pjt@...gle.com, evn@...gle.com, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, peterz@...radead.org,
        pawan.kumar.gupta@...ux.intel.com, kim.phillips@....com,
        alexandre.chartre@...cle.com, daniel.sneddon@...ux.intel.com,
        José Oliveira <joseloliveira11@...il.com>,
        Rodrigo Branco <rodrigo@...nelhacking.com>,
        Alexandra Sandulescu <aesa@...gle.com>,
        Jim Mattson <jmattson@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH RESEND] x86/speculation: Fix user-mode spectre-v2
 protection with KERNEL_IBRS

On Mon, Feb 20, 2023 at 06:46:04PM +0100, Borislav Petkov wrote:
> On Mon, Feb 20, 2023 at 08:34:42AM -0800, Josh Poimboeuf wrote:
> > We will never enable IBRS in user space.  We tried that years ago and it
> > was very slow.
> 
> Then I don't know what this is trying to fix.
> 
> We'd need a proper bug statement in the commit message what the problem
> is. As folks have established, the hw vuln mess is a whole universe of
> crazy. So without proper documenting, this spaghetti madness will be
> completely unreadable.

Agreed, and there seems to be a lot of confusion around this patch.  I
think I understand the issue, let me write up a new patch which is
hopefully clearer.

-- 
Josh