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SubjectRe: [PATCH 5/6] arm64: add sysfs vulnerability show for speculative store bypass
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On 06/12/2018 23:44, Jeremy Linton wrote:
> From: Mian Yousaf Kaukab <ykaukab@suse.de>
>
> Return status based no ssbd_state and the arm64 SSBS feature.
^^ on

> Return string "Unknown" in case CONFIG_ARM64_SSBD is
> disabled or arch workaround2 is not available
> in the firmware.
>
> Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>
> [Added SSBS logic]
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
> arch/arm64/kernel/cpu_errata.c | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 6505c93d507e..8aeb5ca38db8 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -423,6 +423,7 @@ 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;
> @@ -828,4 +829,31 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr,
> }
> }
>
> +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
^^^^ SSBD
> + * 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");

NIT: To me this reads as the mitigation is disabled. Can we call it
"Speculative Store Bypass Disable" (with a capital 'D' and without the
'd at the end)?

Steve

> +
> + case ARM64_SSBD_FORCE_DISABLE:
> + return sprintf(buf, "Vulnerable\n");
> +
> + default: /* ARM64_SSBD_UNKNOWN*/
> + return sprintf(buf, "Unknown\n");
> + }
> +}
> +
> #endif
>

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