Re: [PATCH 10/11] x86/sev: Extend the config-fs attestation support for an SVSM
From: Tom Lendacky
Date: Tue Feb 06 2024 - 13:54:34 EST
On 2/5/24 17:29, Kuppuswamy, Sathyanarayanan wrote:
On 2/1/24 11:10 PM, Dan Williams wrote:
Tom Lendacky wrote:
When an SVSM is present, the guest can also request attestation reports
from the SVSM. These SVSM attestation reports can be used to attest the
SVSM and any services running within the SVSM.
Extend the config-fs attestation support to allow for an SVSM attestation
report. This involves creating four (4) new config-fs attributes:
- 'svsm' (input)
This attribute is used to determine whether the attestation request
should be sent to the SVSM or to the SEV firmware.
- 'service_guid' (input)
Used for requesting the attestation of a single service within the
SVSM. A null GUID implies that the SVSM_ATTEST_SERVICES call should
be used to request the attestation report. A non-null GUID implies
that the SVSM_ATTEST_SINGLE_SERVICE call should be used.
- 'service_version' (input)
Used with the SVSM_ATTEST_SINGLE_SERVICE call, the service version
represents a specific service manifest version be used for the
attestation report.
- 'manifestblob' (output)
Used to return the service manifest associated with the attestation
report.
Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
Documentation/ABI/testing/configfs-tsm | 55 ++++++++++
arch/x86/include/asm/sev.h | 31 +++++-
arch/x86/kernel/sev.c | 50 +++++++++
drivers/virt/coco/sev-guest/sev-guest.c | 137 ++++++++++++++++++++++++
drivers/virt/coco/tsm.c | 95 +++++++++++++++-
include/linux/tsm.h | 11 ++
6 files changed, 376 insertions(+), 3 deletions(-)
diff --git a/Documentation/ABI/testing/configfs-tsm b/Documentation/ABI/testing/configfs-tsm
index dd24202b5ba5..c5423987d323 100644
--- a/Documentation/ABI/testing/configfs-tsm
+++ b/Documentation/ABI/testing/configfs-tsm
@@ -31,6 +31,21 @@ Description:
Standardization v2.03 Section 4.1.8.1 MSG_REPORT_REQ.
https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/56421.pdf
+What: /sys/kernel/config/tsm/report/$name/manifestblob
+Date: January, 2024
+KernelVersion: v6.9
+Contact: linux-coco@xxxxxxxxxxxxxxx
+Description:
+ (RO) Optional supplemental data that a TSM may emit, visibility
+ of this attribute depends on TSM, and may be empty if no
+ manifest data is available.
+
+ When @provider is "sev_guest" and the "svsm" attribute is set
+ this file contains the service manifest used for the SVSM
+ attestation report from Secure VM Service Module for SEV-SNP
+ Guests v1.00 Section 7.
+ https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/58019.pdf
I wish configfs had better dynamic visibility so that this could be
hidden when not active... oh well.
+
What: /sys/kernel/config/tsm/report/$name/provider
Date: September, 2023
KernelVersion: v6.7
@@ -80,3 +95,43 @@ Contact: linux-coco@xxxxxxxxxxxxxxx
Description:
(RO) Indicates the minimum permissible value that can be written
to @privlevel.
+
+What: /sys/kernel/config/tsm/report/$name/svsm
+Date: January, 2024
+KernelVersion: v6.9
+Contact: linux-coco@xxxxxxxxxxxxxxx
+Description:
+ (WO) Attribute is visible if a TSM implementation provider
+ supports the concept of attestation reports for TVMs running
+ under an SVSM, like SEV-SNP. Specifying any non-zero value
Just use kstrtobool just to have a bit more form to it, and who knows
maybe keeping some non-zero numbers reserved turns out useful someday.
...or see below, maybe this shouldn't be an "svsm" flag.
+ implies that the attestation report should come from the SVSM.
+ Secure VM Service Module for SEV-SNP Guests v1.00 Section 7.
+ https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/58019.pdf
So this affects the output format of outblob? I think @outblob should
probably document the fact that it depends on @provider, @privlevel, and
now @svsm. Probably all of the format links should live under @outblob
not @provider.
I worry that "svsm" is not going to be the last name for a selected
family of services that might convey something to outblob. I wonder if
this should just be a generic "service" attribute where "svsm" is only
supported value to write today. Another service family could be
introduced later and reuse the service_guid concept, or kernel gets
lucky and a de-facto standard heads off proliferation here.
+
+What: /sys/kernel/config/tsm/report/$name/service_guid
+Date: January, 2024
+KernelVersion: v6.9
+Contact: linux-coco@xxxxxxxxxxxxxxx
+Description:
+ (WO) Attribute is visible if a TSM implementation provider
+ supports the concept of attestation reports for TVMs running
+ under an SVSM, like SEV-SNP. Specifying a empty or null GUID
+ (00000000-0000-0000-0000-000000) requests all active services
+ within the SVSM be part of the attestation report. Specifying
+ a non-null GUID requests an attestation report of just the
+ specified service using the manifest form specified by the
+ service_version attribute.
+ Secure VM Service Module for SEV-SNP Guests v1.00 Section 7.
+ https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/58019.pdf
Given the small number of service GUIDs so far perhaps save someone the
URL fetch and list it here?
How will user know about the available GUIDs? Is there a way for user to
query this list?
In a sense, yes. You can request an all services attestation which will
return a manifest containing all the active services GUIDs.
+
+What: /sys/kernel/config/tsm/report/$name/service_version
+Date: January, 2024
+KernelVersion: v6.9
+Contact: linux-coco@xxxxxxxxxxxxxxx
+Description:
+ (WO) Attribute is visible if a TSM implementation provider
+ supports the concept of attestation reports for TVMs running
+ under an SVSM, like SEV-SNP. Indicates the service manifest
+ version requested for the attestation report.
+ Secure VM Service Module for SEV-SNP Guests v1.00 Section 7.
+ https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/58019.pdf
Perhaps document that version 1 is assumed and is always compatible?
What prompts new versions and how does that discovered by guest software?
Why user care about it? If it is going to affect manifestblob output, I
recommend adding that info there.
Will do.
Thanks,
Tom