Messages in this thread | | | Date | Fri, 21 Oct 2022 16:12:15 -0500 | Subject | Re: [PATCH Part2 v6 42/49] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event | From | "Kalra, Ashish" <> |
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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)
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) { *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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