linux-kernel - Re: [PATCH 23/35] x86/speculation: Add basic speculation control code

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Date:   Thu, 18 Jan 2018 10:37:45 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH 23/35] x86/speculation: Add basic speculation control code

On Thu, Jan 18, 2018 at 02:48:23PM +0100, Peter Zijlstra wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> Add the minimal infrastructure to control the speculation control feature.
> 
>  - Integrate it into the spectre_v2 coammand line parser and the mitigation
>    selector function. The conditional selector function is a placeholder
>    right now, which needs to be expanded with CPU specific decision
>    functions.
> 
>  - Provide a static key for the actual code control.
> 
>  - Provide a init function which is called after jump label patching is
>    functional.
> 
>  - Provide an interface for the late micro code loader to allow late
>    discovery of the IBRS support. Not yet functional.
> 
> [peterz: fixed Makefile]
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |    1 
>  arch/x86/include/asm/nospec-branch.h            |    5 +++
>  arch/x86/kernel/cpu/Makefile                    |    1 
>  arch/x86/kernel/cpu/bugs.c                      |   26 +++++++++++++++++-
>  arch/x86/kernel/cpu/specctrl.c                  |   33 ++++++++++++++++++++++++
>  5 files changed, 64 insertions(+), 2 deletions(-)
> 
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3932,6 +3932,7 @@
>  			retpoline	  - replace indirect branches
>  			retpoline,generic - google's original retpoline
>  			retpoline,amd     - AMD-specific minimal thunk
> +			ibrs		  - Intel: Indirect Branch Restricted Speculation

Are there plans to add spectre_v2=ibrs_always to prevent SMT-based
attacks?

> --- /dev/null
> +++ b/arch/x86/kernel/cpu/specctrl.c
> @@ -0,0 +1,33 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <asm/cpufeature.h>
> +#include <asm/cpufeatures.h>
> +#include <asm/nospec-branch.h>
> +
> +static inline void specctrl_enable_ibrs(void)
> +{
> +	setup_force_cpu_cap(X86_FEATURE_IBRS);
> +}

"spec_ctrl" seems much more readable than specctrl (for both function
and file names).  And also more consistent with the SPEC_CTRL MSR and
FEATURE names.

-- 
Josh