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

[Tom Lendacky]

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