[PATCH 3/3] 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>
---
 .../ABI/testing/sysfs-devices-system-cpu         |  4 ++++
 arch/x86/coco/sev/core.c                         | 16 +++++++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 63586e299aa8..cec413a71491 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
@@ -700,6 +701,9 @@ Description:	Secure Encrypted Virtualization (SEV) information
 		      the SEV-SNP guest is running. This file is only present
 		      when running as an SEV-SNP guest.
 
+		sev_status: Reports the value of the SEV_STATUS MSR which
+			    enumerates the enabled features of an SEV
+			    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 5770b99feb9b..4532ffc27041 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -1431,9 +1431,23 @@ 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_group sev_attr_group = {};
+static struct attribute *sev_status_attrs[] = {
+	&sev_status_attr.attr,
+	NULL
+};
+
+static struct attribute_group sev_attr_group = {
+	.attrs = sev_status_attrs,
+};
 
 static int __init sev_sysfs_init(void)
 {
-- 
2.53.0