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Date: Mon, 11 Mar 2024 11:16:08 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: "Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@...el.com>,
linux-kernel@...r.kernel.org, x86@...nel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Dan Williams <dan.j.williams@...el.com>, Michael Roth
<michael.roth@....com>, Ashish Kalra <ashish.kalra@....com>
Subject: Re: [PATCH v2 11/14] x86/sev: Extend the config-fs attestation
support for an SVSM
On 3/10/24 00:06, Kuppuswamy, Sathyanarayanan wrote:
>
> On 3/8/24 10:35 AM, 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_manifest_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@....com>
>> ---
>> Documentation/ABI/testing/configfs-tsm | 59 ++++++++++
>> arch/x86/include/asm/sev.h | 31 ++++-
>> arch/x86/kernel/sev.c | 50 ++++++++
>> drivers/virt/coco/sev-guest/sev-guest.c | 147 ++++++++++++++++++++++++
>> drivers/virt/coco/tsm.c | 95 ++++++++++++++-
>> include/linux/tsm.h | 11 ++
>> 6 files changed, 390 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/ABI/testing/configfs-tsm b/Documentation/ABI/testing/configfs-tsm
>> index dd24202b5ba5..a4663610bf7c 100644
>> --- a/Documentation/ABI/testing/configfs-tsm
>> +++ b/Documentation/ABI/testing/configfs-tsm
>> +
>> +What: /sys/kernel/config/tsm/report/$name/svsm
>> +Date: January, 2024
>> +KernelVersion: v6.9
>> +Contact: linux-coco@...ts.linux.dev
>> +Description:
>> + (WO) Attribute is visible if a TSM implementation provider
>> + supports the concept of attestation reports for TVMs running
>> + under an SVSM, like SEV-SNP. Specifying a 1 (or other boolean
>
> Since service_guid can be used for non SVSM services as well, can we use
> a generic term "service" here? And let user specify the service type
> (like service=svsm)
I suppose that's possible. I think we would need a better term than just
service, though, since service_guid is specific to a service within the
service provider... so maybe service_provider.
>
>> + equivalent, e.g. "Y") implies that the attestation report
>> + should come from the SVSM.
>> + Secure VM Service Module for SEV-SNP Guests v1.00 Section 7.
>> + https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/58019.pdf
>> +
>> +What: /sys/kernel/config/tsm/report/$name/service_guid
>> +Date: January, 2024
>> +KernelVersion: v6.9
>> +Contact: linux-coco@...ts.linux.dev
>> +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_manifest_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
>> +
>
> I think it will be useful to the user if there is a attribute to list the service GUIDs
> supported. It can help prevent user using incorrect or unsupported GUIDs.
A list of supported GUIDs can be obtained from the manifest of a
all-services attestation request.
> >> + if (guid_is_null(&desc->service_guid)) {
>> + call_id = SVSM_ATTEST_CALL(SVSM_ATTEST_SERVICES);
>> + } else {
>> + export_guid(attest_call.service_guid, &desc->service_guid);
>> + attest_call.service_manifest_version = desc->service_manifest_version;
>> +
>> + call_id = SVSM_ATTEST_CALL(SVSM_ATTEST_SINGLE_SERVICE);
>> + }
>
> Above initialization will not change during retry, right? Why not move it above
> retry?
True, will move it outside of the loop.
>
>> +
>> + /* Obtain the GUID string length */
>> + guid_len = (len && buf[len - 1] == '\n') ? len - 1 : len;
>> + if (guid_len && guid_len != UUID_STRING_LEN)
>> + return -EINVAL;
>> +
>
> I don't think you need above checks. I think guid_parse will fail, if it is not
> a valid GUID.
Yes and no. The guid_parse() function will succeed if the string is longer
than UUID_STRING_LEN as long as it is a valid UUID up to UUID_STRING_LEN.
In other words, guid_parse() of:
aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee
and
aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee-gg
both succeed.
I'm ok with eliminating the length calculation and check if everyone is in
favor of doing that given the above behavior.
>
>> + if (guid_len == UUID_STRING_LEN) {
>> + rc = guid_parse(buf, &report->desc.service_guid);
>> + if (rc)
>> + return rc;
>> + } else {
>> + report->desc.service_guid = guid_null;
>
> I think the default value will be guid_null right, why reset it to NULL for every failed attempt?
Default, yes. But what if it is written once, then a second time with an
invalid GUID. Should the previously written GUID still be used?
Thanks,
Tom
>
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