Re: [RFC PATCH v1 01/10] KVM: SVM: Add KVM_SEV SEND_START command

Borislav Petkov
2019-04-26T14:10:56Z

On Wed, Apr 24, 2019 at 04:09:59PM +0000, Singh, Brijesh wrote:
> 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>
> ---
> .../virtual/kvm/amd-memory-encryption.rst | 24 +++++
> arch/x86/kvm/svm.c | 101 ++++++++++++++++++
> include/uapi/linux/kvm.h | 12 +++
> 3 files changed, 137 insertions(+)
>
> diff --git a/Documentation/virtual/kvm/amd-memory-encryption.rst b/Documentation/virtual/kvm/amd-memory-encryption.rst
> index 659bbc093b52..340ac4f87321 100644
> --- a/Documentation/virtual/kvm/amd-memory-encryption.rst
> +++ b/Documentation/virtual/kvm/amd-memory-encryption.rst
> @@ -238,6 +238,30 @@ 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_cert_uaddr; /* platform certificate chain */
> + __u32 plat_cert_len;
> +
> + __u64 amd_cert_uaddr; /* AMD certificate */
> + __u32 amd_cert_len;

__u64 session_uaddr;
__u32 session_len;

too, right?

> + };
> +
> References
> ==========
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 406b558abfef..4c2a225ba546 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -6955,6 +6955,104 @@ static int sev_launch_secret(struct kvm *kvm, struct kvm_sev_cmd *argp)
> 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;
> + void *amd_cert = NULL, *session_data = NULL;
> + void *pdh_cert = NULL, *plat_cert = NULL;
> + struct sev_data_send_start *data = NULL;
> + struct kvm_sev_send_start params;
> + 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;
> +
> + data = kzalloc(sizeof(*data), GFP_KERNEL);
> + if (!data)
> + return -ENOMEM;
> +
> + /* userspace wants to query the session length */
> + if (!params.session_len)
> + goto cmd;
> +
> + if (!params.pdh_cert_uaddr || !params.pdh_cert_len ||
> + !params.session_uaddr)
> + return -EINVAL;
> +
> + /* 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;
> + }
> +
> + data->pdh_cert_address = __psp_pa(pdh_cert);
> + data->pdh_cert_len = params.pdh_cert_len;
> +
> + plat_cert = psp_copy_user_blob(params.plat_cert_uaddr, params.plat_cert_len);
> + if (IS_ERR(plat_cert)) {
> + ret = PTR_ERR(plat_cert);
> + goto e_free_pdh;
> + }
> +
> + data->plat_cert_address = __psp_pa(plat_cert);
> + data->plat_cert_len = params.plat_cert_len;
> +
> + amd_cert = psp_copy_user_blob(params.amd_cert_uaddr, params.amd_cert_len);
> + if (IS_ERR(amd_cert)) {
> + ret = PTR_ERR(amd_cert);
> + goto e_free_plat_cert;
> + }
> +
> + data->amd_cert_address = __psp_pa(amd_cert);
> + data->amd_cert_len = params.amd_cert_len;
> +
> + ret = -ENOMEM;
> + session_data = kmalloc(params.session_len, GFP_KERNEL);

If the user is supposed to query the session length first, you could
save it in a global variable perhaps and use that value instead of
trusting the user to give you the correct one in params.session_len for
the allocation...

> + if (!session_data)
> + goto e_free_amd_cert;
> +
> + data->session_address = __psp_pa(session_data);
> + data->session_len = params.session_len;
> +cmd:
> + data->handle = sev->handle;
> + ret = sev_issue_cmd(kvm, SEV_CMD_SEND_START, data, &argp->error);
> +
> + /* if we queried the session length, FW responded with expected data */

<--- ... here you have the session length from the fw.

--
Regards/Gruss,
Boris.

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