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Message-ID: <7fb25176-3752-1be3-66d4-a7f5a0e1617a@amd.com>
Date: Wed, 1 Feb 2023 07:21:08 +1100
From: Alexey Kardashevskiy <aik@....com>
To: Tom Lendacky <thomas.lendacky@....com>,
"Kalra, Ashish" <ashish.kalra@....com>,
Michael Roth <michael.roth@....com>, kvm@...r.kernel.org
Cc: linux-coco@...ts.linux.dev, linux-mm@...ck.org,
linux-crypto@...r.kernel.org, x86@...nel.org,
linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
jroedel@...e.de, hpa@...or.com, ardb@...nel.org,
pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
wanpengli@...cent.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, 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, harald@...fian.com,
Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH RFC v7 52/64] KVM: SVM: Provide support for
SNP_GUEST_REQUEST NAE event
On 01/02/2023 03:23, Tom Lendacky wrote:
> On 1/30/23 19:54, Alexey Kardashevskiy wrote:
>>
>>
>> On 11/1/23 13:01, Kalra, Ashish wrote:
>>> On 1/10/2023 6:48 PM, Alexey Kardashevskiy wrote:
>>>> On 10/1/23 19:33, Kalra, Ashish wrote:
>>>>>
>>>>> On 1/9/2023 8:28 PM, Alexey Kardashevskiy wrote:
>>>>>>
>>>>>>
>>>>>> On 10/1/23 10:41, Kalra, Ashish wrote:
>>>>>>> On 1/8/2023 9:33 PM, Alexey Kardashevskiy wrote:
>>>>>>>> On 15/12/22 06:40, Michael Roth 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>
>>>>>>>>> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
>>>>>>>>> Signed-off-by: Michael Roth <michael.roth@....com>
>>>>>>>>> ---
>>>>>>>>> arch/x86/kvm/svm/sev.c | 185
>>>>>>>>> +++++++++++++++++++++++++++++++++++++++--
>>>>>>>>> arch/x86/kvm/svm/svm.h | 2 +
>>>>>>>>> 2 files changed, 181 insertions(+), 6 deletions(-)
>>>>>>>>>
>>>>>>>>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
>>>>>>>>> index 5f2b2092cdae..18efa70553c2 100644
>>>>>>>>> --- a/arch/x86/kvm/svm/sev.c
>>>>>>>>> +++ b/arch/x86/kvm/svm/sev.c
>>>>>>>>> @@ -331,6 +331,7 @@ static int sev_guest_init(struct kvm *kvm,
>>>>>>>>> struct kvm_sev_cmd *argp)
>>>>>>>>> if (ret)
>>>>>>>>> goto e_free;
>>>>>>>>> + mutex_init(&sev->guest_req_lock);
>>>>>>>>> ret = sev_snp_init(&argp->error, false);
>>>>>>>>> } else {
>>>>>>>>> ret = sev_platform_init(&argp->error);
>>>>>>>>> @@ -2051,23 +2052,34 @@ int sev_vm_move_enc_context_from(struct
>>>>>>>>> kvm *kvm, unsigned int source_fd)
>>>>>>>>> */
>>>>>>>>> static void *snp_context_create(struct kvm *kvm, struct
>>>>>>>>> kvm_sev_cmd *argp)
>>>>>>>>> {
>>>>>>>>> + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>>>>>>>>> struct sev_data_snp_addr data = {};
>>>>>>>>> - void *context;
>>>>>>>>> + void *context, *certs_data;
>>>>>>>>> int rc;
>>>>>>>>> + /* Allocate memory used for the certs data in SNP guest
>>>>>>>>> request */
>>>>>>>>> + certs_data = kzalloc(SEV_FW_BLOB_MAX_SIZE,
>>>>>>>>> GFP_KERNEL_ACCOUNT);
>>>>>>>>> + if (!certs_data)
>>>>>>>>> + return NULL;
>>>>>>>>> +
>>>>>>>>> /* Allocate memory for context page */
>>>>>>>>> context = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT);
>>>>>>>>> if (!context)
>>>>>>>>> - return NULL;
>>>>>>>>> + goto e_free;
>>>>>>>>> data.gctx_paddr = __psp_pa(context);
>>>>>>>>> rc = __sev_issue_cmd(argp->sev_fd,
>>>>>>>>> SEV_CMD_SNP_GCTX_CREATE, &data, &argp->error);
>>>>>>>>> - if (rc) {
>>>>>>>>> - snp_free_firmware_page(context);
>>>>>>>>> - return NULL;
>>>>>>>>> - }
>>>>>>>>> + if (rc)
>>>>>>>>> + goto e_free;
>>>>>>>>> +
>>>>>>>>> + sev->snp_certs_data = certs_data;
>>>>>>>>> return context;
>>>>>>>>> +
>>>>>>>>> +e_free:
>>>>>>>>> + snp_free_firmware_page(context);
>>>>>>>>> + kfree(certs_data);
>>>>>>>>> + return NULL;
>>>>>>>>> }
>>>>>>>>> static int snp_bind_asid(struct kvm *kvm, int *error)
>>>>>>>>> @@ -2653,6 +2665,8 @@ static int
>>>>>>>>> snp_decommission_context(struct kvm *kvm)
>>>>>>>>> snp_free_firmware_page(sev->snp_context);
>>>>>>>>> sev->snp_context = NULL;
>>>>>>>>> + kfree(sev->snp_certs_data);
>>>>>>>>> +
>>>>>>>>> return 0;
>>>>>>>>> }
>>>>>>>>> @@ -3174,6 +3188,8 @@ static int sev_es_validate_vmgexit(struct
>>>>>>>>> vcpu_svm *svm, u64 *exit_code)
>>>>>>>>> case SVM_VMGEXIT_UNSUPPORTED_EVENT:
>>>>>>>>> case SVM_VMGEXIT_HV_FEATURES:
>>>>>>>>> case SVM_VMGEXIT_PSC:
>>>>>>>>> + case SVM_VMGEXIT_GUEST_REQUEST:
>>>>>>>>> + case SVM_VMGEXIT_EXT_GUEST_REQUEST:
>>>>>>>>> break;
>>>>>>>>> default:
>>>>>>>>> reason = GHCB_ERR_INVALID_EVENT;
>>>>>>>>> @@ -3396,6 +3412,149 @@ static int snp_complete_psc(struct
>>>>>>>>> kvm_vcpu *vcpu)
>>>>>>>>> return 1;
>>>>>>>>> }
>>>>>>>>> +static unsigned long snp_setup_guest_buf(struct vcpu_svm *svm,
>>>>>>>>> + struct sev_data_snp_guest_request *data,
>>>>>>>>> + gpa_t req_gpa, gpa_t resp_gpa)
>>>>>>>>> +{
>>>>>>>>> + struct kvm_vcpu *vcpu = &svm->vcpu;
>>>>>>>>> + struct kvm *kvm = vcpu->kvm;
>>>>>>>>> + kvm_pfn_t req_pfn, resp_pfn;
>>>>>>>>> + struct kvm_sev_info *sev;
>>>>>>>>> +
>>>>>>>>> + sev = &to_kvm_svm(kvm)->sev_info;
>>>>>>>>> +
>>>>>>>>> + if (!IS_ALIGNED(req_gpa, PAGE_SIZE) ||
>>>>>>>>> !IS_ALIGNED(resp_gpa, PAGE_SIZE))
>>>>>>>>> + return SEV_RET_INVALID_PARAM;
>>>>>>>>> +
>>>>>>>>> + req_pfn = gfn_to_pfn(kvm, gpa_to_gfn(req_gpa));
>>>>>>>>> + if (is_error_noslot_pfn(req_pfn))
>>>>>>>>> + return SEV_RET_INVALID_ADDRESS;
>>>>>>>>> +
>>>>>>>>> + resp_pfn = gfn_to_pfn(kvm, gpa_to_gfn(resp_gpa));
>>>>>>>>> + if (is_error_noslot_pfn(resp_pfn))
>>>>>>>>> + return SEV_RET_INVALID_ADDRESS;
>>>>>>>>> +
>>>>>>>>> + if (rmp_make_private(resp_pfn, 0, PG_LEVEL_4K, 0, true))
>>>>>>>>> + return SEV_RET_INVALID_ADDRESS;
>>>>>>>>> +
>>>>>>>>> + data->gctx_paddr = __psp_pa(sev->snp_context);
>>>>>>>>> + data->req_paddr = __sme_set(req_pfn << PAGE_SHIFT);
>>>>>>>>> + data->res_paddr = __sme_set(resp_pfn << PAGE_SHIFT);
>>>>>>>>> +
>>>>>>>>> + return 0;
>>>>>>>>> +}
>>>>>>>>> +
>>>>>>>>> +static void snp_cleanup_guest_buf(struct
>>>>>>>>> sev_data_snp_guest_request *data, unsigned long *rc)
>>>>>>>>> +{
>>>>>>>>> + u64 pfn = __sme_clr(data->res_paddr) >> PAGE_SHIFT;
>>>>>>>>> + int ret;
>>>>>>>>> +
>>>>>>>>> + ret = snp_page_reclaim(pfn);
>>>>>>>>> + if (ret)
>>>>>>>>> + *rc = SEV_RET_INVALID_ADDRESS;
>>>>>>>>> +
>>>>>>>>> + ret = rmp_make_shared(pfn, PG_LEVEL_4K);
>>>>>>>>> + if (ret)
>>>>>>>>> + *rc = SEV_RET_INVALID_ADDRESS;
>>>>>>>>> +}
>>>>>>>>> +
>>>>>>>>> +static void snp_handle_guest_request(struct vcpu_svm *svm,
>>>>>>>>> gpa_t req_gpa, gpa_t resp_gpa)
>>>>>>>>> +{
>>>>>>>>> + struct sev_data_snp_guest_request data = {0};
>>>>>>>>> + struct kvm_vcpu *vcpu = &svm->vcpu;
>>>>>>>>> + struct kvm *kvm = vcpu->kvm;
>>>>>>>>> + struct kvm_sev_info *sev;
>>>>>>>>> + unsigned long rc;
>>>>>>>>> + int err;
>>>>>>>>> +
>>>>>>>>> + if (!sev_snp_guest(vcpu->kvm)) {
>>>>>>>>> + rc = SEV_RET_INVALID_GUEST;
>>>>>>>>> + goto e_fail;
>>>>>>>>> + }
>>>>>>>>> +
>>>>>>>>> + sev = &to_kvm_svm(kvm)->sev_info;
>>>>>>>>> +
>>>>>>>>> + mutex_lock(&sev->guest_req_lock);
>>>>>>>>> +
>>>>>>>>> + rc = snp_setup_guest_buf(svm, &data, req_gpa, resp_gpa);
>>>>>>>>> + if (rc)
>>>>>>>>> + goto unlock;
>>>>>>>>> +
>>>>>>>>> + rc = sev_issue_cmd(kvm, SEV_CMD_SNP_GUEST_REQUEST, &data,
>>>>>>>>> &err);
>>>>>>>>
>>>>>>>>
>>>>>>>> This one goes via sev_issue_cmd_external_user() and uses sev-fd...
>>>>>>>>
>>>>>>>>> + if (rc)
>>>>>>>>> + /* use the firmware error code */
>>>>>>>>> + rc = err;
>>>>>>>>> +
>>>>>>>>> + snp_cleanup_guest_buf(&data, &rc);
>>>>>>>>> +
>>>>>>>>> +unlock:
>>>>>>>>> + mutex_unlock(&sev->guest_req_lock);
>>>>>>>>> +
>>>>>>>>> +e_fail:
>>>>>>>>> + svm_set_ghcb_sw_exit_info_2(vcpu, rc);
>>>>>>>>> +}
>>>>>>>>> +
>>>>>>>>> +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;
>>>>>>>>> + }
>>>>>>>>> +
>>>>>>>>> + 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);
>>>>>>>>
>>>>>>>> but this one does not and jump straight to
>>>>>>>> drivers/crypto/ccp/sev-dev.c ignoring sev->fd. Why different?
>>>>>>>> Can these two be unified? sev_issue_cmd_external_user() only
>>>>>>>> checks if fd is /dev/sev which is hardly useful.
>>>>>>>>
>>>>>>>> "[PATCH RFC v7 32/64] crypto: ccp: Provide APIs to query
>>>>>>>> extended attestation report" added this one.
>>>>>>>
>>>>>>> SNP_EXT_GUEST_REQUEST additionally returns a certificate blob and
>>>>>>> that's why it goes through the CCP driver interface
>>>>>>> snp_guest_ext_guest_request() that is used to get both the report
>>>>>>> and certificate data/blob at the same time.
>>>>>>
>>>>>> True. I thought though that this calls for extending
>>>>>> sev_issue_cmd() to take care of these extra parameters rather than
>>>>>> just skipping the sev->fd.
>>>>>>
>>>>>>
>>>>>>> All the FW API calls on the KVM side go through sev_issue_cmd()
>>>>>>> and sev_issue_cmd_external_user() interfaces and that i believe
>>>>>>> uses sev->fd more of as a sanity check.
>>>>>>
>>>>>> Does not look like it:
>>>>>>
>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/crypto/ccp/sev-dev.c?h=v6.2-rc3#n1290
>>>>>>
>>>>>> ===
>>>>>> int sev_issue_cmd_external_user(struct file *filep, unsigned int cmd,
>>>>>> void *data, int *error)
>>>>>> {
>>>>>> if (!filep || filep->f_op != &sev_fops)
>>>>>> return -EBADF;
>>>>>>
>>>>>> return sev_do_cmd(cmd, data, error);
>>>>>> }
>>>>>> EXPORT_SYMBOL_GPL(sev_issue_cmd_external_user);
>>>>>> ===
>>>>>>
>>>>>> The only "more" is that it requires sev->fd to be a valid open fd,
>>>>>> what is the value in that? I may easily miss the bigger picture
>>>>>> here. Thanks,
>>>>>>
>>>>>>
>>>>>
>>>>> Have a look at following functions in drivers/crypto/ccp/sev-dev.c:
>>>>> sev_dev_init() and sev_misc_init().
>>>>>
>>>>> static int sev_misc_init(struct sev_device *sev)
>>>>> {
>>>>> struct device *dev = sev->dev;
>>>>> int ret;
>>>>>
>>>>> /*
>>>>> * SEV feature support can be detected on multiple devices
>>>>> but
>>>>> * the SEV FW commands must be issued on the master. During
>>>>> * probe, we do not know the master hence we create
>>>>> /dev/sev on
>>>>> * the first device probe.
>>>>> * sev_do_cmd() finds the right master device to which to
>>>>> issue
>>>>> * the command to the firmware.
>>>>> */
>>>>
>>>>
>>>> It is still a single /dev/sev node and the userspace cannot get it
>>>> wrong, it does not have to choose between (for instance) /dev/sev0
>>>> and /dev/sev1 on a 2 SOC system.
>>>>
>>>>> ...
>>>>> ...
>>>>>
>>>>> Hence, sev_issue_cmd_external_user() needs to ensure that the
>>>>> correct device (master device) is being operated upon and that's
>>>>> why there is the check for file operations matching sev_fops as
>>>>> below :
>>>>>
>>>>> int sev_issue_cmd_external_user(struct file *filep, unsigned int cmd,
>>>>> void *data, int *error)
>>>>> {
>>>>> if (!filep || filep->f_op != &sev_fops)
>>>>> return -EBADF;
>>>>> ..
>>>>> ..
>>>>>
>>>>> Essentially, sev->fd is the misc. device created for the master PSP
>>>>> device on which the SEV/SNP firmware commands are issued, hence,
>>>>> sev_issue_cmd() uses sev->fd.
>>>>
>>>> There is always just one fd which always uses psp_master, nothing
>>>> from that fd is used.
>>>
>>> It also ensures that we can only issue commands (sev_issue_cmd) after
>>> SEV/SNP guest has launched.
>>
>> I can open /dev/sev and start sending commands to the firmware with no
>> KVM running at all. Oh well, we discussed this offline :)
>>
>>> We don't have a valid fd to use before the guest launch. The file
>>> descriptor is passed as part of the guest launch flow, for example,
>>> in snp_launch_start().
>>>>
>>>> More to the point, if sev->fd is still important, why is it ok to
>>>> skip it for snp_handle_ext_guest_request()? Thanks,
>>>>
>>>>
>>> Then, we should do the same for snp_handle_ext_guest_request().
>>
>> Okay.
>>
>> This snp_handle_ext_guest_request() helper is for returning "Table 21.
>> ATTESTATION_REPORT Structure" along with the certificate(s) used to
>> sign the report: "This usage allows the attestation report and the
>> certificates required to verify the report to be returned at the same
>> time".
>>
>> I can see:
>> 1) KVM_SEV_SNP_{G,S}ET_CERTS ioctls on KVM VM and
>
> This allows the VMM to (optionally) supply per-VM certificates that the
> guest can use to validate the attestation report, instead of the guest
> requesting separately.
>
>> 2) SNP_{SET,GET}_EXT_CONFIG ioctls on /dev/sev
>
> This allows the VMM to (optionally) supply certificates used for all
> VMs, i.e., there is no need for per-VM certificates.
>
>> Both store the passed blob and neither communicate it to the firmware.
>> This makes me wonder - how does the attestation report (cooked by the
>> firmware) get signed with those certificates passed on by the HV
>> userspace?
>
> These are for use by the guest to validate the attestation report. It
> allows the guest to obtain the certificate information without having to
> use another method to request the certificates.
>
> By having this certificate store, the hypervisor can request the
> certificates from the KDS once, rather than every time a guest requests
> an attestation report.
>
>>
>> Also, the cached blob in /dev/sev seems redundand - the attestation
>> report is retuned for a specific guest so having a blob in the KVM VM
>> makes sense and KVM unconditionally reserves memory for it anyway. And
>> for the HV itself the blob is useless (?) so why bother with caching
>> it in /dev/sev.
>
> In general, the certificates are for the machine (VCEK, ASK, ARK), so
> they can be for all VMs on the machine. The per-VM blob allows a VMM to
> supply additional per-VM certficates, if it desires, but is not required.
>
>>
>> And GET ioctls() return what SET passed on (not something the firware
>> returned, for example), what is ever going to call SET? The userspace can
>
> As stated above, the firmware already has the information needed to sign
> the attestation report. The SET IOCTL is used to supply the certficates
> to the guest for validation of the attestation report.
Does the firmware have to have all certificates beforehand? How does the
firmware choose which certificate to use for a specific VM, or just
signs all reports with all certificates it knows?
> This reduces the
> traffic and complexity of the guest requesting the certficates from the
> KDS.
Guest <-> HV interaction is clear, I am only wondering about HV <-> FW.
>> as well cache what it passed and save a bit of the code/memory in the
>> kernel.
>>
>> btw SNP_{SET,GET}_EXT_CONFIG are documented in
>> Documentation/virt/coco/sev-guest.rst but implemented in
>> drivers/crypto/ccp/sev-dev.c (not sev-guest.c).
>>
>> What do I miss in the big picture here? :) Thanks,
>
> The reason for the extended request is to make the attestation request
> appear atomic to the guest. If you had to make two calls to request the
> information, in the future, when live migration is possible, there is no
> guarantee that the guest couldn't have been migrated in between the
> calls to obtain the certificates and the call to obtain the attestation
> report and thus validation of the attestation report could fail.
--
Alexey
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