From: Nuno Das Neves <nunodasneves@xxxxxxxxxxxxxxxxxxx> Sent: Thursday, February 20, 2025 10:33 AM
>
> Introduce hv_current_partition_type to store the partition type
> as an enum.
>
> Right now this is limited to guest or root partition, but there will
> be other kinds in future and the enum is easily extensible.
>
> Set up hv_current_partition_type early in Hyper-V initialization with
> hv_identify_partition_type(). hv_root_partition() just queries this
> value, and shouldn't be called before that.
>
> Making this check into a function sets the stage for adding a config
> option to gate the compilation of root partition code. In particular,
> hv_root_partition() can be stubbed out always be false if root
> partition support isn't desired.
>
>
[snip]
> +void hv_identify_partition_type(void)
> +{
> + /* Assume guest role */
> + hv_current_partition_type = HV_PARTITION_TYPE_GUEST;
> + /*
> + * Check partition creation and cpu management privileges
> + *
> + * Hyper-V should never specify running as root and as a Confidential
> + * VM. But to protect against a compromised/malicious Hyper-V trying
> + * to exploit root behavior to expose Confidential VM memory, ignore
> + * the root partition setting if also a Confidential VM.
> + */
> + if ((ms_hyperv.priv_high & HV_CREATE_PARTITIONS) &&
> + (ms_hyperv.priv_high & HV_CPU_MANAGEMENT) &&
> + !(ms_hyperv.priv_high & HV_ISOLATION)) {
> + pr_info("Hyper-V: running as root partition\n");
> + if (IS_ENABLED(CONFIG_MSHV_ROOT))
I'll have to rescind the "Reviewed-by:" that I just gave. There's a patch
sequencing problem in that CONFIG_MSHV_ROOT doesn't exist yet.
It's added in Patch 3 of the series. Because it doesn't exist, the
IS_ENABLED() will always return 'false', which isn't fatal in the sense
of causing a compile error. But the code won't run in the root partition
because hv_current_partition_type isn't set.
Michael
> + hv_current_partition_type = HV_PARTITION_TYPE_ROOT;
> + else
> + pr_crit("Hyper-V: CONFIG_MSHV_ROOT not enabled!\n");
> + }
> +}
