Date:   Tue, 10 Jan 2023 20:01:27 -0600
From:   "Kalra, Ashish" <ashish.kalra@....com>
To:     Alexey Kardashevskiy <aik@....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, thomas.lendacky@....com, 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 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. 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().

Thanks,
Ashish

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