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SubjectRe: [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@arm.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@arm.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@arm.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

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