Re: [PATCH 01/12] KVM: SVM: Add KVM_SEV SEND_START command

[Steve Rutherford <srutherford@google.com>]

On Wed, Feb 12, 2020 at 5:15 PM Ashish Kalra <Ashish.Kalra@amd.com> wrote:
>
> From: Brijesh Singh <brijesh.singh@amd.com>
>
> The command is used to create an outgoing SEV guest encryption context.
>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: x86@kernel.org
> Cc: kvm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
>  .../virt/kvm/amd-memory-encryption.rst        |  27 ++++
>  arch/x86/kvm/svm.c                            | 125 ++++++++++++++++++
>  include/linux/psp-sev.h                       |   8 +-
>  include/uapi/linux/kvm.h                      |  12 ++
>  4 files changed, 168 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/virt/kvm/amd-memory-encryption.rst b/Documentation/virt/kvm/amd-memory-encryption.rst
> index d18c97b4e140..826911f41f3b 100644
> --- a/Documentation/virt/kvm/amd-memory-encryption.rst
> +++ b/Documentation/virt/kvm/amd-memory-encryption.rst
> @@ -238,6 +238,33 @@ Returns: 0 on success, -negative on error
>                  __u32 trans_len;
>          };
>
> +10. KVM_SEV_SEND_START
> +----------------------
> +
> +The KVM_SEV_SEND_START command can be used by the hypervisor to create an
> +outgoing guest encryption context.
> +
> +Parameters (in): struct kvm_sev_send_start
> +
> +Returns: 0 on success, -negative on error
> +
> +::
> +        struct kvm_sev_send_start {
> +                __u32 policy;                 /* guest policy */
> +
> +                __u64 pdh_cert_uaddr;         /* platform Diffie-Hellman certificate */
> +                __u32 pdh_cert_len;
> +
> +                __u64 plat_certs_uadr;        /* platform certificate chain */
> +                __u32 plat_certs_len;
> +
> +                __u64 amd_certs_uaddr;        /* AMD certificate */
> +                __u32 amd_cert_len;
> +
> +                __u64 session_uaddr;          /* Guest session information */
> +                __u32 session_len;
> +        };
> +
>  References
>  ==========
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index a3e32d61d60c..3a7e2cac51de 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -7140,6 +7140,128 @@ static int sev_launch_secret(struct kvm *kvm, struct kvm_sev_cmd *argp)
>         return ret;
>  }
>
> +/* Userspace wants to query session length. */
> +static int
> +__sev_send_start_query_session_length(struct kvm *kvm, struct kvm_sev_cmd *argp,
> +                                     struct kvm_sev_send_start *params)
> +{
> +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +       struct sev_data_send_start *data;
> +       int ret;
> +
> +       data = kzalloc(sizeof(*data), GFP_KERNEL_ACCOUNT);
> +       if (data == NULL)
> +               return -ENOMEM;
> +
> +       data->handle = sev->handle;
> +       ret = sev_issue_cmd(kvm, SEV_CMD_SEND_START, data, &argp->error);
> +
> +       params->session_len = data->session_len;
> +       if (copy_to_user((void __user *)(uintptr_t)argp->data, params,
> +                               sizeof(struct kvm_sev_send_start)))
> +               ret = -EFAULT;
> +
> +       kfree(data);
> +       return ret;
> +}
> +
> +static int sev_send_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +       struct sev_data_send_start *data;
> +       struct kvm_sev_send_start params;
> +       void *amd_certs, *session_data;
> +       void *pdh_cert, *plat_certs;
> +       int ret;
> +
> +       if (!sev_guest(kvm))
> +               return -ENOTTY;
> +
> +       if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
> +                               sizeof(struct kvm_sev_send_start)))
> +               return -EFAULT;
> +
> +       /* if session_len is zero, userspace wants t query the session length */

/t/to/
>
> +       if (!params.session_len)
> +               return __sev_send_start_query_session_length(kvm, argp,
> +                               &params);
Document this behavior with the command.

> +
> +       /* some sanity checks */
> +       if (!params.pdh_cert_uaddr || !params.pdh_cert_len ||
> +           !params.session_uaddr || params.session_len > SEV_FW_BLOB_MAX_SIZE)
> +               return -EINVAL;
> +
> +       /* allocate the memory to hold the session data blob */
> +       session_data = kmalloc(params.session_len, GFP_KERNEL_ACCOUNT);
> +       if (!session_data)
> +               return -ENOMEM;
> +
> +       /* copy the certificate blobs from userspace */
> +       pdh_cert = psp_copy_user_blob(params.pdh_cert_uaddr,
> +                               params.pdh_cert_len);
> +       if (IS_ERR(pdh_cert)) {
> +               ret = PTR_ERR(pdh_cert);
> +               goto e_free_session;
> +       }
> +
> +       plat_certs = psp_copy_user_blob(params.plat_certs_uaddr,
> +                               params.plat_certs_len);
> +       if (IS_ERR(plat_certs)) {
> +               ret = PTR_ERR(plat_certs);
> +               goto e_free_pdh;
> +       }
> +
> +       amd_certs = psp_copy_user_blob(params.amd_certs_uaddr,
> +                               params.amd_certs_len);
> +       if (IS_ERR(amd_certs)) {
> +               ret = PTR_ERR(amd_certs);
> +               goto e_free_plat_cert;
> +       }
> +
> +       data = kzalloc(sizeof(*data), GFP_KERNEL_ACCOUNT);
> +       if (data == NULL) {
> +               ret = -ENOMEM;
> +               goto e_free_amd_cert;
> +       }
> +
> +       /* populate the FW SEND_START field with system physical address */
> +       data->pdh_cert_address = __psp_pa(pdh_cert);
> +       data->pdh_cert_len = params.pdh_cert_len;
> +       data->plat_certs_address = __psp_pa(plat_certs);
> +       data->plat_certs_len = params.plat_certs_len;
> +       data->amd_certs_address = __psp_pa(amd_certs);
> +       data->amd_certs_len = params.amd_certs_len;
> +       data->session_address = __psp_pa(session_data);
> +       data->session_len = params.session_len;
> +       data->handle = sev->handle;
> +
> +       ret = sev_issue_cmd(kvm, SEV_CMD_SEND_START, data, &argp->error);
sev_issue_cmd can fail. I think you want to handle those errors here
(e.g. it can return -ebadf or a number of others). Right now they
could get clobbered by a later copy_to_user error.

It's also worth documenting what the error argp->error is filled in
with. I didn't see anything in the docs mentioning the status codes
(may have missed it).

> +
> +       if (copy_to_user((void __user *)(uintptr_t) params.session_uaddr,
> +                       session_data, params.session_len)) {
> +               ret = -EFAULT;
> +               goto e_free;
> +       }
> +
> +       params.policy = data->policy;
> +       params.session_len = data->session_len;
> +       if (copy_to_user((void __user *)(uintptr_t)argp->data, &params,
> +                               sizeof(struct kvm_sev_send_start)))
> +               ret = -EFAULT;
> +
> +e_free:
> +       kfree(data);
> +e_free_amd_cert:
> +       kfree(amd_certs);
> +e_free_plat_cert:
> +       kfree(plat_certs);
> +e_free_pdh:
> +       kfree(pdh_cert);
> +e_free_session:
> +       kfree(session_data);
> +       return ret;
> +}
> +
>  static int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
>  {
>         struct kvm_sev_cmd sev_cmd;
> @@ -7181,6 +7303,9 @@ static int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
>         case KVM_SEV_LAUNCH_SECRET:
>                 r = sev_launch_secret(kvm, &sev_cmd);
>                 break;
> +       case KVM_SEV_SEND_START:
> +               r = sev_send_start(kvm, &sev_cmd);
> +               break;
>         default:
>                 r = -EINVAL;
>                 goto out;
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 5167bf2bfc75..9f63b9d48b63 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -323,11 +323,11 @@ struct sev_data_send_start {
>         u64 pdh_cert_address;                   /* In */
>         u32 pdh_cert_len;                       /* In */
>         u32 reserved1;
> -       u64 plat_cert_address;                  /* In */
> -       u32 plat_cert_len;                      /* In */
> +       u64 plat_certs_address;                 /* In */
> +       u32 plat_certs_len;                     /* In */
>         u32 reserved2;
> -       u64 amd_cert_address;                   /* In */
> -       u32 amd_cert_len;                       /* In */
> +       u64 amd_certs_address;                  /* In */
> +       u32 amd_certs_len;                      /* In */
>         u32 reserved3;
>         u64 session_address;                    /* In */
>         u32 session_len;                        /* In/Out */
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 4b95f9a31a2f..17bef4c245e1 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1558,6 +1558,18 @@ struct kvm_sev_dbg {
>         __u32 len;
>  };
>
> +struct kvm_sev_send_start {
> +       __u32 policy;
> +       __u64 pdh_cert_uaddr;
> +       __u32 pdh_cert_len;
> +       __u64 plat_certs_uaddr;
> +       __u32 plat_certs_len;
> +       __u64 amd_certs_uaddr;
> +       __u32 amd_certs_len;
> +       __u64 session_uaddr;
> +       __u32 session_len;
> +};
> +
>  #define KVM_DEV_ASSIGN_ENABLE_IOMMU    (1 << 0)
>  #define KVM_DEV_ASSIGN_PCI_2_3         (1 << 1)
>  #define KVM_DEV_ASSIGN_MASK_INTX       (1 << 2)
> --
> 2.17.1
>

Looks pretty reasonable overall.