[PATCH 2/2] x86/sev: Make SEV_STATUS available via SYSFS

[Joerg Roedel <joro@8bytes.org>]

From: Joerg Roedel <jroedel@suse.de>

Current user-space tooling which needs access to the SEV_STATUS MSR is
using the MSR module. The use of this module poses a security risk in
any trusted execution environment and is generally discouraged.

Instead, provide an file in SYSFS in the /sys/hypervisor/sev/
directory to provide the value of the SEV_STATUS MSR to user-space.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
 Documentation/ABI/testing/sysfs-hypervisor | 5 +++++
 arch/x86/coco/sev/core.c                   | 9 +++++++++
 2 files changed, 14 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-hypervisor b/Documentation/ABI/testing/sysfs-hypervisor
index aca8b02c878c..54c80899c19c 100644
--- a/Documentation/ABI/testing/sysfs-hypervisor
+++ b/Documentation/ABI/testing/sysfs-hypervisor
@@ -1,5 +1,6 @@
 What:		/sys/devices/system/cpu/sev
 		/sys/devices/system/cpu/sev/vmpl
+		/sys/devices/system/cpu/sev/sev_status
 Date:		May 2024
 Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
 Description:	Secure Encrypted Virtualization (SEV) information
@@ -8,3 +9,7 @@ Description:	Secure Encrypted Virtualization (SEV) information
 
 		vmpl: Reports the Virtual Machine Privilege Level (VMPL) at which
 		      the SEV-SNP guest is running.
+
+		sev_status: Reports the value of the SEV_STATUS MSR which
+		            enumerates the enabled features of an SEV-SNP
+			    environment.
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 51a04a19449b..3e834ce9badc 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -2678,10 +2678,19 @@ static ssize_t vmpl_show(struct kobject *kobj,
 	return sysfs_emit(buf, "%d\n", snp_vmpl);
 }
 
+static ssize_t sev_status_show(struct kobject *kobj,
+			       struct kobj_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%llx\n", sev_status);
+}
+
 static struct kobj_attribute vmpl_attr = __ATTR_RO(vmpl);
+static struct kobj_attribute sev_status_attr = __ATTR_RO(sev_status);
+
 
 static struct attribute *vmpl_attrs[] = {
 	&vmpl_attr.attr,
+	&sev_status_attr.attr,
 	NULL
 };
 
-- 
2.48.1