Re: [PATCH RFC v7 52/64] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event
From: Tom Lendacky
Date: Tue Jan 31 2023 - 17:42:35 EST
On 1/31/23 16:00, Alexey Kardashevskiy wrote:
On 01/02/2023 08:21, Tom Lendacky wrote:
On 1/31/23 14:21, Alexey Kardashevskiy wrote:
On 01/02/2023 03:23, Tom Lendacky wrote:
On 1/30/23 19:54, Alexey Kardashevskiy wrote:
On 11/1/23 13:01, Kalra, Ashish wrote:
On 1/10/2023 6:48 PM, Alexey Kardashevskiy wrote:
On 10/1/23 19:33, Kalra, Ashish wrote:
On 1/9/2023 8:28 PM, Alexey Kardashevskiy wrote:
On 10/1/23 10:41, Kalra, Ashish wrote:
On 1/8/2023 9:33 PM, Alexey Kardashevskiy wrote:
On 15/12/22 06:40, Michael Roth wrote:
From: Brijesh Singh <brijesh.singh@xxxxxxx>
Version 2 of GHCB specification added the support for two SNP
Guest
Request Message NAE events. The events allows for an SEV-SNP
guest to
make request to the SEV-SNP firmware through hypervisor using the
SNP_GUEST_REQUEST API define in the SEV-SNP firmware
specification.
The SNP_EXT_GUEST_REQUEST is similar to SNP_GUEST_REQUEST with
the
difference of an additional certificate blob that can be
passed through
the SNP_SET_CONFIG ioctl defined in the CCP driver. The CCP
driver
provides snp_guest_ext_guest_request() that is used by the KVM
to get
both the report and certificate data at once.
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
And GET ioctls() return what SET passed on (not something the firware
returned, for example), what is ever going to call SET? The userspace
can
As stated above, the firmware already has the information needed to
sign the attestation report. The SET IOCTL is used to supply the
certficates to the guest for validation of the attestation report.
Does the firmware have to have all certificates beforehand? How does
the firmware choose which certificate to use for a specific VM, or just
signs all reports with all certificates it knows?
From the SNP API spec, the firmware uses the VCEK, which is derived
from chip-unique secrets, to sign the attestation report.
Does the firmware derive it? How does the guest gets to know it?
(forgive me my ignorance)
Yes, the firmware derives the private key. The guest doesn't know the
private key, it gets the VCEK certificate which has the public key and can
then validate the attestation report.
The guest can then use the returned VCEK certificate, the ASK
certificate and ARK certificate from the extended guest request to
validate the attestation report.
This reduces the traffic and complexity of the guest requesting the
certficates from the KDS.
Guest <-> HV interaction is clear, I am only wondering about HV <-> FW.
I'm not sure what you mean here. The HV doesn't put the signing key in
the firmware, it is derived.
Those ioctls() are in the HV and they take certificates which then get
sent to the guest but not to the firmware. The firmware signs a report
with a key and the guest needs another half of it to verify the report.
Sadly I do not know cryptography enough.
Correct, no need to send the certificates to the firmware. The certs have
the public key which can be used to verify the report signed with the
private key.
Thanks,
Tom