linux-kernel - Re: [PATCH 05/14] arm64: Add 'ssbd' command-line option

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Date:   Tue, 22 May 2018 08:29:24 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Marc Zyngier <marc.zyngier@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu
Cc:     Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoffer Dall <christoffer.dall@....com>
Subject: Re: [PATCH 05/14] arm64: Add 'ssbd' command-line option

On 05/22/2018 08:06 AM, Marc Zyngier wrote:
> On a system where the firmware implements ARCH_WORKAROUND_2,
> it may be useful to either permanently enable or disable the
> workaround for cases where the user decides that they'd rather
> not get a trap overhead, and keep the mitigation permanently
> on or off instead of switching it on exception entry/exit.
> 
> In any case, default to the mitigation being enabled.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  17 ++++
>  arch/arm64/include/asm/cpufeature.h             |   6 ++
>  arch/arm64/kernel/cpu_errata.c                  | 102 ++++++++++++++++++++----
>  3 files changed, 109 insertions(+), 16 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f2040d46f095..646e112c6f63 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4092,6 +4092,23 @@
>  			expediting.  Set to zero to disable automatic
>  			expediting.
>  
> +	ssbd=		[ARM64,HW]
> +			Speculative Store Bypass Disable control
> +
> +			On CPUs that are vulnerable to the Speculative
> +			Store Bypass vulnerability and offer a
> +			firmware based mitigation, this parameter
> +			indicates how the mitigation should be used:
> +
> +			force-on:  Unconditionnaly enable mitigation for

			           Unconditionally

> +				   for both kernel and userspace
> +			force-off: Unconditionnaly disable mitigation for

			           Unconditionally

> +				   for both kernel and userspace
> +			kernel:    Always enable mitigation in the
> +				   kernel, and offer a prctl interface
> +				   to allow userspace to register its
> +				   interest in being mitigated too.
> +
>  	stack_guard_gap=	[MM]
>  			override the default stack gap protection. The value
>  			is in page units and it defines how many pages prior



-- 
~Randy