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

["Jörg Rödel" <joro@8bytes.org>]

From: Joerg Roedel <joerg.roedel@amd.com>

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/devices/system/cpu/sev/
directory to provide the value of the SEV_STATUS MSR to user-space.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
---
 Documentation/ABI/testing/sysfs-devices-system-cpu | 4 ++++
 arch/x86/coco/sev/core.c                           | 8 ++++++++
 2 files changed, 12 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 82d10d556cc8..f7908ade4be8 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -690,6 +690,7 @@ Description:	Umwait control
 
 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
@@ -699,6 +700,9 @@ 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.
 
 What:		/sys/devices/system/cpu/svm
 Date:		August 2019
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 7ed3da998489..557c1f230cb9 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -1435,10 +1435,18 @@ 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, "0x%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
 };
 
-- 
2.53.0