Re: [PATCH 4/6] arm64: add sysfs vulnerability show for spectre v2

[Julien Thierry <julien.thierry@arm.com>]

On 06/12/2018 23:44, Jeremy Linton wrote:
> Add code to track whether all the cores in the machine are
> vulnerable, and whether all the vulnerable cores have been
> mitigated.
> 
> Once we have that information we can add the sysfs stub and
> provide an accurate view of what is known about the machine.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
>  arch/arm64/kernel/cpu_errata.c | 72 +++++++++++++++++++++++++++++++---
>  1 file changed, 67 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 559ecdee6fd2..6505c93d507e 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c

[...]

> @@ -766,4 +812,20 @@ ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr,
>  	return sprintf(buf, "Mitigation: __user pointer sanitization\n");
>  }
>  
> +ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
> +		char *buf)
> +{
> +	switch (__spectrev2_safe) {
> +	case A64_SV2_SAFE:
> +		return sprintf(buf, "Not affected\n");
> +	case A64_SV2_UNSAFE:
> +		if (__hardenbp_enab == A64_HBP_MIT)
> +			return sprintf(buf,
> +				"Mitigation: Branch predictor hardening\n");
> +		return sprintf(buf, "Vulnerable\n");
> +	default:
> +		return sprintf(buf, "Unknown\n");
> +	}

Again I see that we are going to display "Unknown" when the mitigation
is not built in.

Couldn't we make that CONFIG_GENERIC_CPU_VULNERABILITIES check whether a
CPU is vulnerable or not even if the mitigation is not implemented? It's
just checking the list of MIDRs.

Thanks,

-- 
Julien Thierry