[PATCH v2 10/10] powerpc/64s: Wire up cpu_show_spectre_v2()

[Diana Madalina Craciun]

Why is the speculation barrier specific to Spectre v2? Can't the barrier
be used as a mitigation for Spectre v1 as well?

Regards,
Diana

On 3/27/2018 3:32 PM, Michael Ellerman wrote:
> Add a definition for cpu_show_spectre_v2() to override the generic
> version. This has several permuations, though in practice some may not
> occur we cater for any combination.
>
> The most verbose is:
>
>   Mitigation: Indirect branch serialisation (kernel only), Indirect
>   branch cache disabled, ori31 speculation barrier enabled
>
> We don't treat the ori31 speculation barrier as a mitigation on its
> own, because it has to be *used* by code in order to be a mitigation
> and we don't know if userspace is doing that. So if that's all we see
> we say:
>
>   Vulnerable, ori31 speculation barrier enabled
>
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> ---
>  arch/powerpc/kernel/security.c | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
>
> diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
> index 0eace3cac818..2cee3dcd231b 100644
> --- a/arch/powerpc/kernel/security.c
> +++ b/arch/powerpc/kernel/security.c
> @@ -58,3 +58,36 @@ ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr, c
>  
>  	return sprintf(buf, "Vulnerable\n");
>  }
> +
> +ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	bool bcs, ccd, ori;
> +	struct seq_buf s;
> +
> +	seq_buf_init(&s, buf, PAGE_SIZE - 1);
> +
> +	bcs = security_ftr_enabled(SEC_FTR_BCCTRL_SERIALISED);
> +	ccd = security_ftr_enabled(SEC_FTR_COUNT_CACHE_DISABLED);
> +	ori = security_ftr_enabled(SEC_FTR_SPEC_BAR_ORI31);
> +
> +	if (bcs || ccd) {
> +		seq_buf_printf(&s, "Mitigation: ");
> +
> +		if (bcs)
> +			seq_buf_printf(&s, "Indirect branch serialisation (kernel only)");
> +
> +		if (bcs && ccd)
> +			seq_buf_printf(&s, ", ");
> +
> +		if (ccd)
> +			seq_buf_printf(&s, "Indirect branch cache disabled");
> +	} else
> +		seq_buf_printf(&s, "Vulnerable");
> +
> +	if (ori)
> +		seq_buf_printf(&s, ", ori31 speculation barrier enabled");
> +
> +	seq_buf_printf(&s, "\n");
> +
> +	return s.len;
> +}