On 3/29/24 17:58, Michael Roth wrote:
Version 2 of GHCB specification added support for the SNP Extended Guest
Request Message NAE event. This event serves a nearly identical purpose
to the previously-added SNP_GUEST_REQUEST event, but allows for
additional certificate data to be supplied via an additional
guest-supplied buffer to be used mainly for verifying the signature of
an attestation report as returned by firmware.
This certificate data is supplied by userspace, so unlike with
SNP_GUEST_REQUEST events, SNP_EXTENDED_GUEST_REQUEST events are first
forwarded to userspace via a KVM_EXIT_VMGEXIT exit type, and then the
firmware request is made only afterward.
Implement handling for these events.
Since there is a potential for race conditions where the
userspace-supplied certificate data may be out-of-sync relative to the
reported TCB or VLEK that firmware will use when signing attestation
reports, make use of the synchronization mechanisms wired up to the
SNP_{PAUSE,RESUME}_ATTESTATION SEV device ioctls such that the guest
will be told to retry the request while attestation has been paused due
to an update being underway on the system.
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
Documentation/virt/kvm/api.rst | 26 ++++++++++++
arch/x86/include/asm/sev.h | 4 ++
arch/x86/kvm/svm/sev.c | 75 ++++++++++++++++++++++++++++++++++
arch/x86/kvm/svm/svm.h | 3 ++
arch/x86/virt/svm/sev.c | 21 ++++++++++
include/uapi/linux/kvm.h | 6 +++
6 files changed, 135 insertions(+)
+static int snp_complete_ext_guest_req(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+ struct vmcb_control_area *control;
+ struct kvm *kvm = vcpu->kvm;
+ sev_ret_code fw_err = 0;
+ int vmm_ret;
+
+ vmm_ret = vcpu->run->vmgexit.ext_guest_req.ret;
+ if (vmm_ret) {
+ if (vmm_ret == SNP_GUEST_VMM_ERR_INVALID_LEN)
+ vcpu->arch.regs[VCPU_REGS_RBX] =
+ vcpu->run->vmgexit.ext_guest_req.data_npages;
+ goto abort_request;
+ }
+
+ control = &svm->vmcb->control;
+
+ if (!__snp_handle_guest_req(kvm, control->exit_info_1, control->exit_info_2,
+ &fw_err))
+ vmm_ret = SNP_GUEST_VMM_ERR_GENERIC;
+
+ /*
+ * Give errors related to stale transactions precedence to provide more
+ * potential options for servicing firmware while guests are running.
+ */
+ if (snp_transaction_is_stale(svm->snp_transaction_id))
+ vmm_ret = SNP_GUEST_VMM_ERR_BUSY;
I think having this after the call to the SEV firmware will cause an
issue. If the firmware has performed the attestation request
successfully in the __snp_handle_guest_req() call, then it will have
incremented the sequence number. If you return busy, then the sev-guest
driver will attempt to re-issue the request with the original sequence
number which will now fail. That failure will then be propagated back to
the sev-guest driver which will then disable the VMPCK key.
So I think you need to put this before the call to firmware.
Thanks,
Tom
+
