linux-kernel - Re: [PATCH 1/1] x86: deduplicate the spectre_v2

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Message-ID: <202109111413.D988175207@keescook>
Date:   Sat, 11 Sep 2021 14:13:36 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        YiFei Zhu <zhuyifei1999@...il.com>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        YiFei Zhu <yifeifz2@...inois.edu>, bpf <bpf@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Andy Lutomirski <luto@...capital.net>,
        David Laight <David.Laight@...lab.com>,
        Dimitrios Skarlatos <dskarlat@...cmu.edu>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Hubertus Franke <frankeh@...ibm.com>,
        Jack Chen <jianyan2@...inois.edu>,
        Jann Horn <jannh@...gle.com>,
        Josep Torrellas <torrella@...inois.edu>,
        Tianyin Xu <tyxu@...inois.edu>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Tycho Andersen <tycho@...ho.pizza>,
        Valentin Rothberg <vrothber@...hat.com>,
        Will Drewry <wad@...omium.org>, Jiri Kosina <jikos@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/1] x86: deduplicate the spectre_v2_user documentation

On Wed, Nov 04, 2020 at 07:14:06PM -0500, Andrea Arcangeli wrote:
> This would need updating to make prctl be the new default, but it's
> simpler to delete it and refer to the dup.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>

I'll take this too.

-Kees

> ---
>  Documentation/admin-guide/hw-vuln/spectre.rst | 51 +------------------
>  1 file changed, 2 insertions(+), 49 deletions(-)
> 
> diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst
> index 19b897cb1d45..ab7d402c1677 100644
> --- a/Documentation/admin-guide/hw-vuln/spectre.rst
> +++ b/Documentation/admin-guide/hw-vuln/spectre.rst
> @@ -593,61 +593,14 @@ kernel command line.
>  		Not specifying this option is equivalent to
>  		spectre_v2=auto.
>  
> -For user space mitigation:
> -
> -        spectre_v2_user=
> -
> -		[X86] Control mitigation of Spectre variant 2
> -		(indirect branch speculation) vulnerability between
> -		user space tasks
> -
> -		on
> -			Unconditionally enable mitigations. Is
> -			enforced by spectre_v2=on
> -
> -		off
> -			Unconditionally disable mitigations. Is
> -			enforced by spectre_v2=off
> -
> -		prctl
> -			Indirect branch speculation is enabled,
> -			but mitigation can be enabled via prctl
> -			per thread. The mitigation control state
> -			is inherited on fork.
> -
> -		prctl,ibpb
> -			Like "prctl" above, but only STIBP is
> -			controlled per thread. IBPB is issued
> -			always when switching between different user
> -			space processes.
> -
> -		seccomp
> -			Same as "prctl" above, but all seccomp
> -			threads will enable the mitigation unless
> -			they explicitly opt out.
> -
> -		seccomp,ibpb
> -			Like "seccomp" above, but only STIBP is
> -			controlled per thread. IBPB is issued
> -			always when switching between different
> -			user space processes.
> -
> -		auto
> -			Kernel selects the mitigation depending on
> -			the available CPU features and vulnerability.
> -
> -		Default mitigation:
> -		If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
> -
> -		Not specifying this option is equivalent to
> -		spectre_v2_user=auto.
> -
>  		In general the kernel by default selects
>  		reasonable mitigations for the current CPU. To
>  		disable Spectre variant 2 mitigations, boot with
>  		spectre_v2=off. Spectre variant 1 mitigations
>  		cannot be disabled.
>  
> +For spectre_v2_user see :doc:`/admin-guide/kernel-parameters`.
> +
>  Mitigation selection guide
>  --------------------------
>  
> 

-- 
Kees Cook