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From:   KP Singh <kpsingh@kernel.org>
Date:   Mon, 20 Feb 2023 10:56:38 -0800
Message-ID: <CACYkzJ5w_ey7aHxhGr-1gpQLPPtRAQLApHiJp_Kh0cOW4PTQkA@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
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On Mon, Feb 20, 2023 at 10:52 AM Borislav Petkov <bp@alien8.de> wrote:
>
> On Mon, Feb 20, 2023 at 10:44:21AM -0800, KP Singh wrote:
> > No it cannot with IBRS which is really just KERNEL_IBRS enabled, we
>
> See my other reply. The intent is there to be able to do it. What needs
> to be figured out now is *why* we said no STIBP with IBRS? Was it an
> omission or was there some intent behind it.
>

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.

STIBP with IBRS is still correct if spectre_v2=ibrs had really meant
IBRS everywhere, but just means KERNEL_IBRS, which means only kernel
is protected, userspace is still unprotected.

> --
> Regards/Gruss,
>     Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette