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Message-ID: <ad2c2d30-0b67-69ec-d4bb-3521784fda5e@amd.com>
Date: Fri, 21 Oct 2022 16:12:15 -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
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)
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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