Re: [PATCH v6 01/14] KVM: SVM: Add KVM_SEV SEND_START command

[Venu Busireddy]

On 2020-03-30 06:19:59 +0000, Ashish Kalra wrote:
> From: Brijesh Singh <Brijesh.Singh@xxxxxxx>
> 
> The command is used to create an outgoing SEV guest encryption context.
> 
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
> Cc: Joerg Roedel <joro@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: kvm@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Reviewed-by: Steve Rutherford <srutherford@xxxxxxxxxx>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> ---
>  .../virt/kvm/amd-memory-encryption.rst        |  27 ++++
>  arch/x86/kvm/svm.c                            | 128 ++++++++++++++++++
>  include/linux/psp-sev.h                       |   8 +-
>  include/uapi/linux/kvm.h                      |  12 ++
>  4 files changed, 171 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/virt/kvm/amd-memory-encryption.rst b/Documentation/virt/kvm/amd-memory-encryption.rst
> index c3129b9ba5cb..4fd34fc5c7a7 100644
> --- a/Documentation/virt/kvm/amd-memory-encryption.rst
> +++ b/Documentation/virt/kvm/amd-memory-encryption.rst
> @@ -263,6 +263,33 @@ 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 */

Could this please be changed to plat_certs_uaddr, as it is referred to
in the rest of the code?

> +                __u32 plat_certs_len;
> +
> +                __u64 amd_certs_uaddr;        /* AMD certificate */
> +                __u32 amd_cert_len;

Could this please be changed to amd_certs_len, as it is referred to in
the rest of the code?

> +
> +                __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 50d1ebafe0b3..63d172e974ad 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -7149,6 +7149,131 @@ 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 to query the session length */
> +	if (!params.session_len)
> +		return __sev_send_start_query_session_length(kvm, argp,
> +				&params);
> +
> +	/* 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);
> +
> +	if (ret)
> +		goto e_free;
> +
> +	if (copy_to_user((void __user *)(uintptr_t) params.session_uaddr,
> +			session_data, params.session_len)) {
> +		ret = -EFAULT;
> +		goto e_free;
> +	}

To optimize the amount of data being copied to user space, could the
above section of code changed as follows?

	params.session_len = data->session_len;
	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;

Since the only fields that are changed in the kvm_sev_send_start structure
are session_len and policy, why do we need to copy the entire structure
back to the user? Why not just those two values? Please see the changes
proposed to kvm_sev_send_start structure further below to accomplish this.

	params.policy = data->policy;
	if (copy_to_user((void __user *)(uintptr_t)argp->data, &params,
			sizeof(params.policy) + sizeof(params.session_len))
		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;
> @@ -7193,6 +7318,9 @@ 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;
> +};

Redo this structure as below:

struct kvm_sev_send_start {
	__u32 policy;
	__u32 session_len;
	__u64 session_uaddr;
	__u64 pdh_cert_uaddr;
	__u32 pdh_cert_len;
	__u64 plat_certs_uaddr;
	__u32 plat_certs_len;
	__u64 amd_certs_uaddr;
	__u32 amd_certs_len;
};

Or as below, just to make it look better.

struct kvm_sev_send_start {
	__u32 policy;
	__u32 session_len;
	__u64 session_uaddr;
	__u32 pdh_cert_len;
	__u64 pdh_cert_uaddr;
	__u32 plat_certs_len;
	__u64 plat_certs_uaddr;
	__u32 amd_certs_len;
	__u64 amd_certs_uaddr;
};

> +
>  #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
>