Re: [PATCH v3 6/7] arm64: add sysfs vulnerability show for speculative store bypass

[Marc Zyngier]

On 09/01/2019 23:55, Jeremy Linton wrote:
> Return status based on ssbd_state and the arm64 SSBS feature. If
> the mitigation is disabled, or the firmware isn't responding then
> return the expected machine state based on a new blacklist of known
> vulnerable cores.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@xxxxxxx>
> ---
>  arch/arm64/kernel/cpu_errata.c | 48 ++++++++++++++++++++++++++++++++++
>  1 file changed, 48 insertions(+)
> 
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index ee286d606d9b..c8ff96158b94 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -288,6 +288,7 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
>  DEFINE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required);
>  
>  int ssbd_state __read_mostly = ARM64_SSBD_KERNEL;
> +static bool __ssb_safe = true;
>  
>  static const struct ssbd_options {
>  	const char	*str;
> @@ -385,10 +386,18 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
>  {
>  	struct arm_smccc_res res;
>  	bool required = true;
> +	bool is_vul;
>  	s32 val;
>  
>  	WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
>  
> +	is_vul = is_midr_in_range_list(read_cpuid_id(), entry->midr_range_list);
> +
> +	if (is_vul)
> +		__ssb_safe = false;
> +
> +	arm64_requested_vuln_attrs |= VULN_SSB;
> +
>  	if (this_cpu_has_cap(ARM64_SSBS)) {
>  		required = false;
>  		goto out_printmsg;
> @@ -422,6 +431,7 @@ 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;
> @@ -476,6 +486,17 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
>  
>  	return required;
>  }
> +
> +/* known vulnerable cores */
> +static const struct midr_range arm64_ssb_cpus[] = {
> +	MIDR_ALL_VERSIONS(MIDR_CORTEX_A57),
> +	MIDR_ALL_VERSIONS(MIDR_CORTEX_A72),
> +	MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
> +	MIDR_ALL_VERSIONS(MIDR_CORTEX_A75),
> +	MIDR_ALL_VERSIONS(MIDR_CORTEX_A76),
> +	{},
> +};
> +
>  #endif	/* CONFIG_ARM64_SSBD */
>  
>  static void __maybe_unused
> @@ -762,6 +783,7 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
>  		.capability = ARM64_SSBD,
>  		.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,
>  		.matches = has_ssbd_mitigation,
> +		.midr_range_list = arm64_ssb_cpus,
>  	},
>  #endif
>  #ifdef CONFIG_ARM64_ERRATUM_1188873
> @@ -809,4 +831,30 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
>  	return sprintf(buf, "Vulnerable\n");
>  }
>  
> +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
> +	 *  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");
> +	}
> +
> +	if (__ssb_safe)
> +		return sprintf(buf, "Not affected\n");

The kbuild robot reports that this fails if CONFIG_ARM64_SSBD is not
selected. What should we print in this case? "Vulnerable"? Or "Unknown"?

> +
> +	return sprintf(buf, "Vulnerable\n");
> +}
> +
>  #endif
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...