Messages in this thread | | | Date | Fri, 21 Oct 2022 16:30:42 -0500 | Subject | Re: [PATCH Part2 v6 42/49] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event | From | Tom Lendacky <> |
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On 10/21/22 16:12, Kalra, Ashish wrote: > Hello Tom, > > On 10/21/2022 2:06 PM, Tom Lendacky wrote: >> On 6/20/22 18:13, Ashish Kalra wrote: >>> From: Brijesh Singh <brijesh.singh@amd.com> >>> >>> 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@amd.com> >>> --- >>> 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? >> > > Agreed. > > The check should probably be > if ((data_npages << PAGE_SHIFT) < SEV_FW_BLOB_MAX_SIZE)
No, the check should just be removed. If the number of pages required to hold the cert data is only 1, then a data_npages value of 1 is just fine (see below).
> > and that check already exists in: > > snp_guest_ext_guest_request(...) > { > ... > ... > /* > * Check if there is enough space to copy the certificate chain. > Otherwise > * return ERROR code defined in the GHCB specification. > */ > expected_npages = sev->snp_certs_len >> PAGE_SHIFT; > if (*npages < expected_npages) {
If expected_npages is 1, then an *npages value of 1 is OK. But if you put the check in above that you want, you would never get here with an *npages value of 1.
Thanks, Tom
> *npages = expected_npages; > *fw_err = SNP_GUEST_REQ_INVALID_LEN; > return -EINVAL; > } > ... > > Thanks, > Ashish > >> 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); >>> +} >>> +
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