linux-kernel - Re: [PATCH v4 10/12] arm64: add sysfs vulnerability show for spectre v2

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Message-ID: <20190131175535.3a632ba5@donnerap.cambridge.arm.com>
Date:   Thu, 31 Jan 2019 17:55:35 +0000
From:   Andre Przywara <andre.przywara@....com>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, stefan.wahren@...e.com,
        mlangsdo@...hat.com, suzuki.poulose@....com, marc.zyngier@....com,
        catalin.marinas@....com, julien.thierry@....com,
        will.deacon@....com, linux-kernel@...r.kernel.org,
        steven.price@....com, ykaukab@...e.de, dave.martin@....com,
        shankerd@...eaurora.org
Subject: Re: [PATCH v4 10/12] arm64: add sysfs vulnerability show for
 spectre v2

On Fri, 25 Jan 2019 12:07:09 -0600
Jeremy Linton <jeremy.linton@....com> wrote:

Hi,

> 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@....com>
> ---
>  arch/arm64/kernel/cpu_errata.c | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 024c83ffff99..caedf268c972 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -497,6 +497,10 @@ cpu_enable_cache_maint_trap(const struct arm64_cpu_capabilities *__unused)
> 	.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,			\
> 	CAP_MIDR_RANGE_LIST(midr_list)
> 
> +/* Track overall mitigation state. We are only mitigated if all cores are ok */
> +static bool __hardenbp_enab = true;
> +static bool __spectrev2_safe = true;
> +
>  /*
>   * List of CPUs that do not need any Spectre-v2 mitigation at all.
>   */
> @@ -507,6 +511,10 @@ static const struct midr_range spectre_v2_safe_list[] = {
> 	{ /* sentinel */ }
>  };
>  
> +/*
> + * Track overall bp hardening for all heterogeneous cores in the machine.
> + * We are only considered "safe" if all booted cores are known safe.
> + */
>  static bool __maybe_unused
>  check_branch_predictor(const struct arm64_cpu_capabilities *entry, int scope)
>  {
> @@ -528,12 +536,19 @@ check_branch_predictor(const struct arm64_cpu_capabilities *entry, int scope)
>  	if (!need_wa)
>  		return false;
>  
> -	if (need_wa < 0)
> +	__spectrev2_safe = false;
> +
> +	if (need_wa < 0) {
>  		pr_warn_once("ARM_SMCCC_ARCH_WORKAROUND_1 missing from firmware\n");
> +		__hardenbp_enab = false;
> +	}
>  
>  	/* forced off */
> -	if (__nospectre_v2)
> +	if (__nospectre_v2) {
> +		pr_info_once("spectrev2 mitigation disabled by command line option\n");
> +		__hardenbp_enab = false;
>  		return false;
> +	}
>  
>  	return (need_wa > 0);
>  }
> @@ -757,4 +772,16 @@ 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)

w/s issue. Other than that:

Reviewed-by: Andre Przywara <andre.przywara@....com>

Cheers,
Andre.

> +{
> +	if (__spectrev2_safe)
> +		return sprintf(buf, "Not affected\n");
> +
> +	if (__hardenbp_enab)
> +		return sprintf(buf, "Mitigation: Branch predictor hardening\n");
> +
> +	return sprintf(buf, "Vulnerable\n");
> +}
> +
>  #endif