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

[Tom Lendacky <thomas.lendacky@amd.com>]

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@evilplan.org>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>   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
>