Re: [PATCH 08/11] x86/sev: Provide guest VMPL level to userspace

[Dionna Amalie Glaze]

On Fri, Jan 26, 2024 at 2:19 PM Tom Lendacky <thomas.lendacky@xxxxxxx> wrote:
>
> Requesting an attestation report from userspace involves providing the
> VMPL level for the report. Currently any value from 0-3 is valid because
> Linux enforces running at VMPL0.
>
> When an SVSM is present, though, Linux will not be running at VMPL0 and
> only VMPL values starting at the VMPL level Linux is running at to 3 are
> valid. In order to allow userspace to determine the minimum VMPL value
> that can be supplied to an attestation report, create a sysfs entry that
> can be used to retrieve the current VMPL level of Linux.

Is this not the intended meaning of privlevel_floor in
/sys/kernel/config/tsm/report/$report0/privlevel_floor?

>
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
>  arch/x86/kernel/sev.c | 37 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
>
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 121a9bad86c9..9844c772099c 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -2479,3 +2479,40 @@ void __init snp_remap_svsm_ca(void)
>         /* Update the CAA to a proper kernel address */
>         boot_svsm_caa = &boot_svsm_ca_page;
>  }
> +
> +static ssize_t vmpl_show(struct kobject *kobj,
> +                        struct kobj_attribute *attr, char *buf)
> +{
> +       return sysfs_emit(buf, "%d\n", vmpl);
> +}
> +
> +static struct kobj_attribute vmpl_attr = __ATTR_RO(vmpl);
> +
> +static struct attribute *vmpl_attrs[] = {
> +       &vmpl_attr.attr,
> +       NULL
> +};
> +
> +static struct attribute_group sev_attr_group = {
> +       .attrs = vmpl_attrs,
> +};
> +
> +static int __init sev_sysfs_init(void)
> +{
> +       struct kobject *sev_kobj;
> +       int ret;
> +
> +       if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> +               return -ENODEV;
> +
> +       sev_kobj = kobject_create_and_add("sev", kernel_kobj);
> +       if (!sev_kobj)
> +               return -ENOMEM;
> +
> +       ret = sysfs_create_group(sev_kobj, &sev_attr_group);
> +       if (ret)
> +               kobject_put(sev_kobj);
> +
> +       return ret;
> +}
> +arch_initcall(sev_sysfs_init);
> --
> 2.42.0
>
>


-- 
-Dionna Glaze, PhD (she/her)