MIME-Version: 1.0
References: <CACYkzJ5L9MLuE5Jz+z5-NJCCrUqTbgKQkXSqnQnCfTD_WNA7_Q@mail.gmail.com>
 <CACYkzJ6n=-tobhX0ONQhjHSgmnNjWnNe_dZnEOGtD8Y6S3RHbA@mail.gmail.com>
 <20230220163442.7fmaeef3oqci4ee3@treble> <Y/Ox3MJZF1Yb7b6y@zn.tnic>
 <20230220175929.2laflfb2met6y3kc@treble> <CACYkzJ71xqzY6-wL+YShcL+d6ugzcdFHr6tbYWWE_ep52+RBZQ@mail.gmail.com>
 <Y/O6Wr4BbtfhXrNt@zn.tnic> <CACYkzJ4jvOGGhuQ1HDzfpGS5vffg9X6hEcLC93QJBFqX+LxLVw@mail.gmail.com>
 <Y/PBSncEMTiO5scL@zn.tnic> <CACYkzJ5w_ey7aHxhGr-1gpQLPPtRAQLApHiJp_Kh0cOW4PTQkA@mail.gmail.com>
 <Y/PDqpwY3sF29PuM@zn.tnic>
In-Reply-To: <Y/PDqpwY3sF29PuM@zn.tnic>
From:   KP Singh <kpsingh@kernel.org>
Date:   Mon, 20 Feb 2023 11:10:46 -0800
Message-ID: <CACYkzJ4jAqDfSvdbNqMbmnQW6eyFj4qtknW1Wq_mm0kHUjOYyA@mail.gmail.com>
Subject: Re: [PATCH RESEND] x86/speculation: Fix user-mode spectre-v2
 protection with KERNEL_IBRS
To:     Borislav Petkov <bp@alien8.de>
Cc:     Josh Poimboeuf <jpoimboe@kernel.org>, linux-kernel@vger.kernel.org,
        pjt@google.com, evn@google.com, tglx@linutronix.de,
        mingo@redhat.com, dave.hansen@linux.intel.com, x86@kernel.org,
        hpa@zytor.com, peterz@infradead.org,
        pawan.kumar.gupta@linux.intel.com, kim.phillips@amd.com,
        alexandre.chartre@oracle.com, daniel.sneddon@linux.intel.com,
        =?UTF-8?Q?Jos=C3=A9_Oliveira?= <joseloliveira11@gmail.com>,
        Rodrigo Branco <rodrigo@kernelhacking.com>,
        Alexandra Sandulescu <aesa@google.com>,
        Jim Mattson <jmattson@google.com>, stable@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Mon, Feb 20, 2023 at 11:02 AM Borislav Petkov <bp@alien8.de> wrote:
>
> 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.

As you said in the other thread, this needs to be documented both in
the code and the kernel documentation.

>
> > 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