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

[Steven Price]

On 06/12/2018 23:44, Jeremy Linton wrote:
> From: Mian Yousaf Kaukab <ykaukab@xxxxxxx>
> 
> Return status based no ssbd_state and the arm64 SSBS feature.
                      ^^ on

> 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@xxxxxxx>
> [Added SSBS logic]
> Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx>
> ---
>  arch/arm64/kernel/cpu_errata.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 6505c93d507e..8aeb5ca38db8 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -423,6 +423,7 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
>  		ssbd_state = ARM64_SSBD_UNKNOWN;
>  		return false;
>  
> +	/* machines with mixed mitigation requirements must not return this */
>  	case SMCCC_RET_NOT_REQUIRED:
>  		pr_info_once("%s mitigation not required\n", entry->desc);
>  		ssbd_state = ARM64_SSBD_MITIGATED;
> @@ -828,4 +829,31 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
>  	}
>  }
>  
> +ssize_t cpu_show_spec_store_bypass(struct device *dev,
> +		struct device_attribute *attr, char *buf)
> +{
> +	/*
> +	 *  Two assumptions: First, get_ssbd_state() reflects the worse case
> +	 *  for hetrogenous machines, and that if SSBS is supported its
                                                  ^^^^ SSBD
> +	 *  supported by all cores.
> +	 */
> +	switch (arm64_get_ssbd_state()) {
> +	case ARM64_SSBD_MITIGATED:
> +		return sprintf(buf, "Not affected\n");
> +
> +	case ARM64_SSBD_KERNEL:
> +	case ARM64_SSBD_FORCE_ENABLE:
> +		if (cpus_have_cap(ARM64_SSBS))
> +			return sprintf(buf, "Not affected\n");
> +		return sprintf(buf,
> +			"Mitigation: Speculative Store Bypass disabled\n");

NIT: To me this reads as the mitigation is disabled. Can we call it
"Speculative Store Bypass Disable" (with a capital 'D' and without the
'd at the end)?

Steve

> +
> +	case ARM64_SSBD_FORCE_DISABLE:
> +		return sprintf(buf, "Vulnerable\n");
> +
> +	default: /* ARM64_SSBD_UNKNOWN*/
> +		return sprintf(buf, "Unknown\n");
> +	}
> +}
> +
>  #endif
>