Re: [PATCH v3 13/14] x86/sev: Hide SVSM attestation entries if not running under an SVSM

From: Kuppuswamy Sathyanarayanan
Date: Tue Apr 09 2024 - 14:13:16 EST



On 3/25/24 3:26 PM, 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 | 14 ++++++++++----
> include/linux/cc_platform.h | 8 ++++++++
> 3 files changed, 22 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 46f230bf13ac..d30471874e87 100644
> --- a/drivers/virt/coco/tsm.c
> +++ b/drivers/virt/coco/tsm.c
> @@ -64,6 +64,12 @@ static struct tsm_report_state *to_state(struct tsm_report *report)
> return container_of(report, struct tsm_report_state, report);
> }
>
> +static bool provider_visibility(const struct config_item *item,
> + const struct configfs_attribute *attr)
> +{
> + return cc_platform_has(CC_ATTR_GUEST_SVSM_PRESENT);
> +}
> +

Any comment about the following query? I think introducing a CC flag for this use
case is over kill.

https://lore.kernel.org/lkml/6b90b223-46e0-4e6d-a17c-5caf72e3c949@xxxxxxxxxxxxxxx/

> static int try_advance_write_generation(struct tsm_report *report)
> {
> struct tsm_report_state *state = to_state(report);
> @@ -144,7 +150,7 @@ static ssize_t tsm_report_service_provider_store(struct config_item *cfg,
>
> return len;
> }
> -CONFIGFS_ATTR_WO(tsm_report_, service_provider);
> +CONFIGFS_ATTR_VISIBLE_WO(tsm_report_, service_provider, provider_visibility);
>
> static ssize_t tsm_report_service_guid_store(struct config_item *cfg,
> const char *buf, size_t len)
> @@ -165,7 +171,7 @@ 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, provider_visibility);
>
> static ssize_t tsm_report_service_manifest_version_store(struct config_item *cfg,
> const char *buf, size_t len)
> @@ -186,7 +192,7 @@ 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, provider_visibility);
>
> static ssize_t tsm_report_inblob_write(struct config_item *cfg,
> const void *buf, size_t count)
> @@ -333,7 +339,7 @@ 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, provider_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

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer