From 61564d346809aa84729e651b98032592a7d63d3e Mon Sep 17 00:00:00 2001 From: Tom Lendacky Date: Wed, 5 Jun 2024 10:18:50 -0500 Subject: [PATCH] x86/sev: Provide guest VMPL level to userspace 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 the kernel. [ bp: Add CONFIG_SYSFS ifdeffery. ] Signed-off-by: Tom Lendacky Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/fff846da0d8d561f9fdaf297dcf8cd907545a25b.1717600736.git.thomas.lendacky@amd.com --- .../ABI/testing/sysfs-devices-system-cpu | 12 +++++ arch/x86/kernel/sev.c | 46 +++++++++++++++++++ 2 files changed, 58 insertions(+) diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index e7e160954e798e..8fd7ed9aee4edb 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -605,6 +605,18 @@ Description: Umwait control Note that a value of zero means there is no limit. Low order two bits must be zero. +What: /sys/devices/system/cpu/sev + /sys/devices/system/cpu/sev/vmpl +Date: May 2024 +Contact: Linux kernel mailing list +Description: Secure Encrypted Virtualization (SEV) information + + This directory is only present when running as an SEV-SNP guest. + + vmpl: Reports the Virtual Machine Privilege Level (VMPL) at which + the SEV-SNP guest is running. + + What: /sys/devices/system/cpu/svm Date: August 2019 Contact: Linux kernel mailing list diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index 84f37315563584..4dc7ae33eac9ee 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -2504,3 +2504,49 @@ void __init snp_update_svsm_ca(void) /* Update the CAA to a proper kernel address */ boot_svsm_caa = &boot_svsm_ca_page; } + +#ifdef CONFIG_SYSFS +static ssize_t vmpl_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%d\n", snp_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; + struct device *dev_root; + int ret; + + if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP)) + return -ENODEV; + + dev_root = bus_get_dev_root(&cpu_subsys); + if (!dev_root) + return -ENODEV; + + sev_kobj = kobject_create_and_add("sev", &dev_root->kobj); + put_device(dev_root); + + 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); +#endif // CONFIG_SYSFS