Re: [PATCH Part2 v6 42/49] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event

[Tom Lendacky]

On 6/20/22 18:13, Ashish Kalra 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>
> ---
>   arch/x86/kvm/svm/sev.c | 196 +++++++++++++++++++++++++++++++++++++++--
>   arch/x86/kvm/svm/svm.h |   2 +
>   2 files changed, 192 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 7fc0fad87054..089af21a4efe 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c

> +static void snp_handle_ext_guest_request(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp_gpa)
> +{
> +	struct sev_data_snp_guest_request req = {0};
> +	struct kvm_vcpu *vcpu = &svm->vcpu;
> +	struct kvm *kvm = vcpu->kvm;
> +	unsigned long data_npages;
> +	struct kvm_sev_info *sev;
> +	unsigned long rc, err;
> +	u64 data_gpa;
> +
> +	if (!sev_snp_guest(vcpu->kvm)) {
> +		rc = SEV_RET_INVALID_GUEST;
> +		goto e_fail;
> +	}
> +
> +	sev = &to_kvm_svm(kvm)->sev_info;
> +
> +	data_gpa = vcpu->arch.regs[VCPU_REGS_RAX];
> +	data_npages = vcpu->arch.regs[VCPU_REGS_RBX];
> +
> +	if (!IS_ALIGNED(data_gpa, PAGE_SIZE)) {
> +		rc = SEV_RET_INVALID_ADDRESS;
> +		goto e_fail;
> +	}
> +
> +	/* Verify that requested blob will fit in certificate buffer */
> +	if ((data_npages << PAGE_SHIFT) > SEV_FW_BLOB_MAX_SIZE) {

Not sure this is a valid check...  Isn't it OK if the guest has supplied 
more room than is required? If the guest supplies 8 pages and the 
hypervisor only needs to copy 1 page of data (or the SEV_FW_BLOB_MAX_SIZE 
number of pages) that shouldn't be an error. I think this check can go, right?

Thanks,
Tom

> +		rc = SEV_RET_INVALID_PARAM;
> +		goto e_fail;
> +	}
> +
> +	mutex_lock(&sev->guest_req_lock);
> +
> +	rc = snp_setup_guest_buf(svm, &req, req_gpa, resp_gpa);
> +	if (rc)
> +		goto unlock;
> +
> +	rc = snp_guest_ext_guest_request(&req, (unsigned long)sev->snp_certs_data,
> +					 &data_npages, &err);
> +	if (rc) {
> +		/*
> +		 * If buffer length is small then return the expected
> +		 * length in rbx.
> +		 */
> +		if (err == SNP_GUEST_REQ_INVALID_LEN)
> +			vcpu->arch.regs[VCPU_REGS_RBX] = data_npages;
> +
> +		/* pass the firmware error code */
> +		rc = err;
> +		goto cleanup;
> +	}
> +
> +	/* Copy the certificate blob in the guest memory */
> +	if (data_npages &&
> +	    kvm_write_guest(kvm, data_gpa, sev->snp_certs_data, data_npages << PAGE_SHIFT))
> +		rc = SEV_RET_INVALID_ADDRESS;
> +
> +cleanup:
> +	snp_cleanup_guest_buf(&req, &rc);
> +
> +unlock:
> +	mutex_unlock(&sev->guest_req_lock);
> +
> +e_fail:
> +	svm_set_ghcb_sw_exit_info_2(vcpu, rc);
> +}
> +