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Date: Fri, 21 Oct 2022 16:56:09 -0500
From: "Kalra, Ashish" <ashish.kalra@....com>
To: Tom Lendacky <thomas.lendacky@....com>, x86@...nel.org,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
linux-coco@...ts.linux.dev, linux-mm@...ck.org,
linux-crypto@...r.kernel.org
Cc: tglx@...utronix.de, mingo@...hat.com, jroedel@...e.de,
hpa@...or.com, ardb@...nel.org, pbonzini@...hat.com,
seanjc@...gle.com, vkuznets@...hat.com, jmattson@...gle.com,
luto@...nel.org, dave.hansen@...ux.intel.com, slp@...hat.com,
pgonda@...gle.com, peterz@...radead.org,
srinivas.pandruvada@...ux.intel.com, rientjes@...gle.com,
dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de,
michael.roth@....com, vbabka@...e.cz, kirill@...temov.name,
ak@...ux.intel.com, tony.luck@...el.com, marcorr@...gle.com,
sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
dgilbert@...hat.com, jarkko@...nel.org
Subject: Re: [PATCH Part2 v6 42/49] KVM: SVM: Provide support for
SNP_GUEST_REQUEST NAE event
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@....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@....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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