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

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Message-ID: <Y/PDqpwY3sF29PuM@zn.tnic>
Date:   Mon, 20 Feb 2023 20:02:02 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     KP Singh <kpsingh@...nel.org>
Cc:     Josh Poimboeuf <jpoimboe@...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 10:56:38AM -0800, KP Singh wrote:
> Sure, it looks like an omission to me, we wrote a POC on Skylake that
> was able to do cross-thread training with the current set of
> mitigations.

Right.

> STIBP with IBRS is still correct if spectre_v2=ibrs had really meant
> IBRS everywhere,

Yeah, IBRS everywhere got shot down as a no-no very early in the game,
for apparent reasons.

> but just means KERNEL_IBRS, which means only kernel is protected,
> userspace is still unprotected.

Yes, that was always the intent with IBRS: enable on kernel entry and
disable on exit.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette