Re: [PATCH v2 13/14] x86/sev: Hide SVSM attestation entries if not running under an SVSM

From: Tom Lendacky
Date: Mon Mar 25 2024 - 12:13:56 EST


On 3/23/24 12:24, Kuppuswamy, Sathyanarayanan wrote:

On 3/8/24 10:35 AM, Tom Lendacky wrote:
Config-fs provides support to hide individual attribute entries. Using
this support, base the display of the SVSM related entries on the presence
of an SVSM.

Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
arch/x86/coco/core.c | 4 ++++
drivers/virt/coco/tsm.c | 13 +++++++++----
include/linux/cc_platform.h | 8 ++++++++
3 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
index d07be9d05cd0..efa0f648f754 100644
--- a/arch/x86/coco/core.c
+++ b/arch/x86/coco/core.c
@@ -12,6 +12,7 @@
#include <asm/coco.h>
#include <asm/processor.h>
+#include <asm/sev.h>
enum cc_vendor cc_vendor __ro_after_init = CC_VENDOR_NONE;
u64 cc_mask __ro_after_init;
@@ -78,6 +79,9 @@ static bool noinstr amd_cc_platform_has(enum cc_attr attr)
case CC_ATTR_GUEST_STATE_ENCRYPT:
return sev_status & MSR_AMD64_SEV_ES_ENABLED;
+ case CC_ATTR_GUEST_SVSM_PRESENT:
+ return snp_get_vmpl();
+
/*
* With SEV, the rep string I/O instructions need to be unrolled
* but SEV-ES supports them through the #VC handler.
diff --git a/drivers/virt/coco/tsm.c b/drivers/virt/coco/tsm.c
index 07b4c95ce704..2efa6e578477 100644
--- a/drivers/virt/coco/tsm.c
+++ b/drivers/virt/coco/tsm.c
@@ -64,6 +64,11 @@ static struct tsm_report_state *to_state(struct tsm_report *report)
return container_of(report, struct tsm_report_state, report);
}
+static umode_t svsm_visibility(const struct config_item *item, const struct configfs_attribute *attr)
+{
+ return cc_platform_has(CC_ATTR_GUEST_SVSM_PRESENT) ? attr->ca_mode : 0;
+}
+

Instead of directly checking for CC flags here, I am wondering if it would make
sense to add a callback to vendor drivers and let the callback decide whether
the attribute is valid or not? We can't add a CC flag for every ConfigFS attribute,
right? For example, privlevel is not used by TDX. If there is a callback, then
TDX driver can make this attribute invalid for it.

I think that's something that can be looked at after this series.

Thanks,
Tom


static int try_advance_write_generation(struct tsm_report *report)
{
struct tsm_report_state *state = to_state(report);
@@ -139,7 +144,7 @@ static ssize_t tsm_report_svsm_store(struct config_item *cfg,
return len;
}
-CONFIGFS_ATTR_WO(tsm_report_, svsm);
+CONFIGFS_ATTR_VISIBLE_WO(tsm_report_, svsm, svsm_visibility);
static ssize_t tsm_report_service_guid_store(struct config_item *cfg,
const char *buf, size_t len)
@@ -168,7 +173,7 @@ static ssize_t tsm_report_service_guid_store(struct config_item *cfg,
return len;
}
-CONFIGFS_ATTR_WO(tsm_report_, service_guid);
+CONFIGFS_ATTR_VISIBLE_WO(tsm_report_, service_guid, svsm_visibility);
static ssize_t tsm_report_service_manifest_version_store(struct config_item *cfg,
const char *buf, size_t len)
@@ -189,7 +194,7 @@ static ssize_t tsm_report_service_manifest_version_store(struct config_item *cfg
return len;
}
-CONFIGFS_ATTR_WO(tsm_report_, service_manifest_version);
+CONFIGFS_ATTR_VISIBLE_WO(tsm_report_, service_manifest_version, svsm_visibility);
static ssize_t tsm_report_inblob_write(struct config_item *cfg,
const void *buf, size_t count)
@@ -336,7 +341,7 @@ static ssize_t tsm_report_manifestblob_read(struct config_item *cfg, void *buf,
return tsm_report_read(report, buf, count, TSM_MANIFEST);
}
-CONFIGFS_BIN_ATTR_RO(tsm_report_, manifestblob, NULL, TSM_OUTBLOB_MAX);
+CONFIGFS_BIN_ATTR_VISIBLE_RO(tsm_report_, manifestblob, NULL, TSM_OUTBLOB_MAX, svsm_visibility);
#define TSM_DEFAULT_ATTRS() \
&tsm_report_attr_generation, \
diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
index cb0d6cd1c12f..f1b4266c1484 100644
--- a/include/linux/cc_platform.h
+++ b/include/linux/cc_platform.h
@@ -90,6 +90,14 @@ enum cc_attr {
* Examples include TDX Guest.
*/
CC_ATTR_HOTPLUG_DISABLED,
+
+ /**
+ * @CC_ATTR_GUEST_SVSM_PRESENT: Guest is running under an SVSM
+ *
+ * The platform/OS is running as a guest/virtual machine and is
+ * running under a Secure VM Service Module (SVSM).
+ */
+ CC_ATTR_GUEST_SVSM_PRESENT,
};
#ifdef CONFIG_ARCH_HAS_CC_PLATFORM