[PATCH 0/3 v2] x86/sev: Report MSR_AMD64_SEV in SYSFS

[PATCH 0/3 v2] x86/sev: Report MSR_AMD64_SEV in SYSFS

[Jörg Rödel]

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

Hi,

Here is an updated version of my original patch to report
MSR_AMD64_SEV in SYSFS. The intention is to give user-space tooling a
way to access the MSR value without needing to expose all MSRs via
the msr.ko module.

The patches here are updated to address a Sashiko comment asking why
SEV_STATUS is only reported for SEV-SNP guests. The sev_status file is
now created for SEV and SEV-ES guests as well.

Please review.

Thanks,

	Joerg

Joerg Roedel (3):
  x86/coco: Add CC_ATTR_GUEST_SEV
  x86/sev: Create /sys/devices/system/cpu/sev/ for all SEV guests
  x86/coco/sev: Make SEV_STATUS available via SYSFS

 .../ABI/testing/sysfs-devices-system-cpu      |  9 +++--
 arch/x86/coco/core.c                          |  3 ++
 arch/x86/coco/sev/core.c                      | 33 ++++++++++++++++---
 include/linux/cc_platform.h                   |  9 +++++
 4 files changed, 47 insertions(+), 7 deletions(-)

-- 
2.53.0

[PATCH 1/3] x86/coco: Add CC_ATTR_GUEST_SEV

[Jörg Rödel]

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

Add a new attribute to the CC platform code to check whether the
kernel runs in an environment using SEV memory encryption. This will
be used to establish the an sev/ directory in SYSFS (which is
currently SEV-SNP-only).

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
---
 arch/x86/coco/core.c        | 3 +++
 include/linux/cc_platform.h | 9 +++++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
index 989ca9f72ba3..63c06c2ac409 100644
--- a/arch/x86/coco/core.c
+++ b/arch/x86/coco/core.c
@@ -95,6 +95,9 @@ static bool noinstr amd_cc_platform_has(enum cc_attr attr)
 		return (sev_status & MSR_AMD64_SEV_ENABLED) &&
 			!(sev_status & MSR_AMD64_SEV_ES_ENABLED);
 
+	case CC_ATTR_GUEST_SEV:
+		return sev_status & MSR_AMD64_SEV_ENABLED;
+
 	case CC_ATTR_GUEST_SEV_SNP:
 		return sev_status & MSR_AMD64_SEV_SNP_ENABLED;
 
diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
index 559353ad64ac..f87ee0652b04 100644
--- a/include/linux/cc_platform.h
+++ b/include/linux/cc_platform.h
@@ -73,6 +73,15 @@ enum cc_attr {
 	 */
 	CC_ATTR_GUEST_UNROLL_STRING_IO,
 
+	/**
+	 * @CC_ATTR_GUEST_SEV: Guest SEV is active.
+	 *
+	 * The platform/OS is running as a virtual machine guest and actively
+	 * using AMD SEV memory encryption. This is true for SEV, SEV-ES, and
+	 * SEV-SNP guests.
+	 */
+	CC_ATTR_GUEST_SEV,
+
 	/**
 	 * @CC_ATTR_GUEST_SEV_SNP: Guest SNP is active.
 	 *
-- 
2.53.0

[PATCH 2/3] x86/sev: Create /sys/devices/system/cpu/sev/ for all SEV guests

[Jörg Rödel]

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

The SYSFS directory for SEV is only created for SEV-SNP guests right
now. Change it to create it for SEV and SEV-ES guests as well so
attributes available on all versions of SEV have a place.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
---
 .../ABI/testing/sysfs-devices-system-cpu      |  5 ++--
 arch/x86/coco/sev/core.c                      | 29 ++++++++++++-------
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 82d10d556cc8..63586e299aa8 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -694,10 +694,11 @@ Date:		May 2024
 Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
 Description:	Secure Encrypted Virtualization (SEV) information
 
-		This directory is only present when running as an SEV-SNP guest.
+		This directory is only present when running as an SEV guest.
 
 		vmpl: Reports the Virtual Machine Privilege Level (VMPL) at which
-		      the SEV-SNP guest is running.
+		      the SEV-SNP guest is running. This file is only present
+		      when running as an SEV-SNP guest.
 
 
 What:		/sys/devices/system/cpu/svm
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index ecd77d3217f3..5770b99feb9b 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -1433,14 +1433,7 @@ static ssize_t vmpl_show(struct kobject *kobj,
 
 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 struct attribute_group sev_attr_group = {};
 
 static int __init sev_sysfs_init(void)
 {
@@ -1448,7 +1441,7 @@ static int __init sev_sysfs_init(void)
 	struct device *dev_root;
 	int ret;
 
-	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+	if (!cc_platform_has(CC_ATTR_GUEST_SEV))
 		return -ENODEV;
 
 	dev_root = bus_get_dev_root(&cpu_subsys);
@@ -1463,9 +1456,25 @@ static int __init sev_sysfs_init(void)
 
 	ret = sysfs_create_group(sev_kobj, &sev_attr_group);
 	if (ret)
-		kobject_put(sev_kobj);
+		goto drop_kobj;
+
+	/* Add SEV-SNP specific attributes */
+	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP)) {
+		/* VMPL */
+		ret = sysfs_add_file_to_group(sev_kobj, &vmpl_attr.attr, NULL);
+		if (ret)
+			goto drop_sysfs;
+	}
+
+	return 0;
+
+drop_sysfs:
+	sysfs_remove_group(sev_kobj, &sev_attr_group);
+drop_kobj:
+	kobject_put(sev_kobj);
 
 	return ret;
+
 }
 arch_initcall(sev_sysfs_init);
 #endif // CONFIG_SYSFS
-- 
2.53.0

[PATCH 3/3] x86/coco/sev: Make SEV_STATUS available via SYSFS

[Jörg Rödel]

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