linux-kernel - Re: [PATCH RESEND 5/6] arm64: add sysfs vulnerability show for speculative store bypass

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Date:   Mon, 17 Sep 2018 14:30:44 +0100
From:   Will Deacon <will.deacon@....com>
To:     Mian Yousaf Kaukab <ykaukab@...e.de>
Cc:     marc.zyngier@....com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, robert.richter@...ium.com,
        cwu@...erecomputing.com
Subject: Re: [PATCH RESEND 5/6] arm64: add sysfs vulnerability show for
 speculative store bypass

On Mon, Aug 27, 2018 at 04:33:09PM +0200, Mian Yousaf Kaukab wrote:
> Return status based no ssbd_state. Return string "Unknown" in case
> CONFIG_ARM64_SSBD is disabled or arch workaround2 is not available
> in the firmware.
> 
> Signed-off-by: Mian Yousaf Kaukab <ykaukab@...e.de>
> ---
>  arch/arm64/kernel/cpu_errata.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 8469d3be7b15..8b60aa30a3fa 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -744,4 +744,24 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
>  	return sprintf(buf, "Not affected\n");
>  }
>  
> +ssize_t cpu_show_spec_store_bypass(struct device *dev,
> +		struct device_attribute *attr, char *buf)
> +{
> +	switch (arm64_get_ssbd_state()) {
> +	case ARM64_SSBD_MITIGATED:
> +		return sprintf(buf, "Not affected\n");
> +
> +	case ARM64_SSBD_KERNEL:
> +	case ARM64_SSBD_FORCE_ENABLE:
> +		return sprintf(buf,
> +			"Mitigation: Speculative Store Bypass disabled");
> +
> +	case ARM64_SSBD_FORCE_DISABLE:
> +		return sprintf(buf, "Vulnerable\n");
> +
> +	default: /* ARM64_SSBD_UNKNOWN*/
> +		return sprintf(buf, "Unknown\n");
> +	}
> +}

This probably wants extending for CPUs that support SSBS (see
for-next/core).

Will