Messages in this thread |  | | Date | Fri, 21 Oct 2022 16:56:09 -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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On 10/21/2022 4:30 PM, Tom Lendacky wrote: > 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). >
Ok.
>> >> 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.
Yes that is correct, i incorrectly assumed that sev->snp_certs_len == SEV_FW_BLOB_MAX_SIZE
Thanks, Ashish
> > 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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