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From:   KP Singh <kpsingh@kernel.org>
Date:   Tue, 21 Feb 2023 11:35:29 -0800
Message-ID: <CACYkzJ7pLhJ+NfUq36PaMxadkgv-cPtO60TW=g_Nh7vU1vEWqA@mail.gmail.com>
Subject: Re: [PATCH v2 1/2] x86/speculation: Allow enabling STIBP with legacy IBRS
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, pjt@google.com, evn@google.com,
        jpoimboe@kernel.org, tglx@linutronix.de, 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,
        corbet@lwn.net, bp@suse.de, linyujun809@huawei.com,
        jmattson@google.com,
        =?UTF-8?Q?Jos=C3=A9_Oliveira?= <joseloliveira11@gmail.com>,
        Rodrigo Branco <rodrigo@kernelhacking.com>,
        Alexandra Sandulescu <aesa@google.com>, stable@vger.kernel.org
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On Tue, Feb 21, 2023 at 11:29 AM Greg KH <gregkh@linuxfoundation.org> wrote=
:
>
> On Tue, Feb 21, 2023 at 07:49:07PM +0100, KP Singh wrote:
> > Setting the IBRS bit implicitly enables STIBP to protect against
> > cross-thread branch target injection. With enhanced IBRS, the bit it se=
t
> > once and is not cleared again. However, on CPUs with just legacy IBRS,
> > IBRS bit set on user -> kernel and cleared on kernel -> user (a.k.a
> > KERNEL_IBRS). Clearing this bit also disables the implicitly enabled
> > STIBP, thus requiring some form of cross-thread protection in userspace=
.
> >
> > Enable STIBP, either opt-in via prctl or seccomp, or always on dependin=
g
> > on the choice of mitigation selected via spectre_v2_user.
> >
> > Reported-by: Jos=C3=A9 Oliveira <joseloliveira11@gmail.com>
> > Reported-by: Rodrigo Branco <rodrigo@kernelhacking.com>
> > Reviewed-by: Alexandra Sandulescu <aesa@google.com>
> > Fixes: 7c693f54c873 ("x86/speculation: Add spectre_v2=3Dibrs option to =
support Kernel IBRS")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: KP Singh <kpsingh@kernel.org>
> > ---
> >  arch/x86/kernel/cpu/bugs.c | 33 ++++++++++++++++++++++-----------
> >  1 file changed, 22 insertions(+), 11 deletions(-)
>
> Why isn't patch 2/2 for stable as well?

It should be. I actually forgot to remove stable from the first one as
there are still ongoing discussions and people kept having to "drop
stable".  I can send a v3 with stable Cc'ed. Should it have a fixes
tag too?

>
> thanks,
>
> greg k-h