Re: [PATCH Part2 v5 42/45] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event

[Peter Gonda <pgonda@google.com>]

On Fri, Aug 20, 2021 at 10:01 AM Brijesh Singh <brijesh.singh@amd.com> wrote:
>
> 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 | 197 +++++++++++++++++++++++++++++++++++++++--
>  arch/x86/kvm/svm/svm.h |   2 +
>  2 files changed, 193 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 712e8907bc39..81ccad412e55 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -19,6 +19,7 @@
>  #include <linux/trace_events.h>
>  #include <linux/sev.h>
>  #include <linux/ksm.h>
> +#include <linux/sev-guest.h>
>  #include <asm/fpu/internal.h>
>
>  #include <asm/pkru.h>
> @@ -338,6 +339,7 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
>
>                 init_srcu_struct(&sev->psc_srcu);
>                 ret = sev_snp_init(&argp->error);
> +               mutex_init(&sev->guest_req_lock);
>         } else {
>                 ret = sev_platform_init(&argp->error);
>         }
> @@ -1602,23 +1604,39 @@ static int sev_receive_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
>
>  static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  {
> +       void *context = NULL, *certs_data = NULL, *resp_page = NULL;
> +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
>         struct sev_data_snp_gctx_create data = {};
> -       void *context;
>         int rc;
>
> +       /* Allocate memory used for the certs data in SNP guest request */
> +       certs_data = kmalloc(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;
> +
> +       /* Allocate a firmware buffer used during the guest command handling. */
> +       resp_page = snp_alloc_firmware_page(GFP_KERNEL_ACCOUNT);
> +       if (!resp_page)
> +               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)
> @@ -2248,6 +2266,8 @@ 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;
>  }
>
> @@ -2746,6 +2766,8 @@ 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:
>                 goto vmgexit_err;
> @@ -3161,6 +3183,155 @@ static unsigned long snp_handle_page_state_change(struct vcpu_svm *svm)
>         return rc ? map_to_psc_vmgexit_code(rc) : 0;
>  }
>
> +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);
> +       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;
> +       }
> +
> +       /* Verify that requested blob will fit in certificate buffer */
> +       if ((data_npages << PAGE_SHIFT) > SEV_FW_BLOB_MAX_SIZE) {
> +               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);
> +}
> +
>  static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
>  {
>         struct vmcb_control_area *control = &svm->vmcb->control;
> @@ -3404,6 +3575,20 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
>                 svm_set_ghcb_sw_exit_info_2(vcpu, rc);
>                 break;
>         }
> +       case SVM_VMGEXIT_GUEST_REQUEST: {
> +               snp_handle_guest_request(svm, control->exit_info_1, control->exit_info_2);
> +
> +               ret = 1;
> +               break;
> +       }
> +       case SVM_VMGEXIT_EXT_GUEST_REQUEST: {
> +               snp_handle_ext_guest_request(svm,
> +                                            control->exit_info_1,
> +                                            control->exit_info_2);
> +
> +               ret = 1;
> +               break;
> +       }

Don't we need some sort of rate limiting here? Since the PSP is a
shared resource that the host needs access to as well as other guests
it seems a little dangerous to let the guest spam this interface.

>         case SVM_VMGEXIT_UNSUPPORTED_EVENT:
>                 vcpu_unimpl(vcpu,
>                             "vmgexit: unsupported event - exit_info_1=%#llx, exit_info_2=%#llx\n",
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 280072995306..71fe46a778f3 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -92,6 +92,8 @@ struct kvm_sev_info {
>         u64 snp_init_flags;
>         void *snp_context;      /* SNP guest context page */
>         struct srcu_struct psc_srcu;
> +       void *snp_certs_data;
> +       struct mutex guest_req_lock;
>  };
>
>  struct kvm_svm {
> --
> 2.17.1
>