Re: [PATCH 1/2] x86/sev: Add KVM commands for instance certs

["Kalra, Ashish" <ashish.kalra@amd.com>]

Hello Dionna,

On 9/1/2022 7:04 PM, Dionna Glaze wrote:
> The /dev/sev device has the ability to store host-wide certificates for
> the key used by the AMD-SP for SEV-SNP attestation report signing,
> but for hosts that want to specify additional certificates that are
> specific to the image launched in a VM, we need a different way to
> communicate those certificates.
> 
> This patch adds two new KVM ioctl commands: KVM_SEV_SNP_{GET,SET}_CERTS
> 
> The certificates that are set with this command are expected to follow
> the same format as the host certificates, but that format is opaque
> to the kernel.
> 
> The new behavior for custom certificates is that the extended guest
> request command will now return the overridden certificates if they
> were installed for the instance. The error condition for a too small
> data buffer is changed to return the overridden certificate data size
> if there is an overridden certificate set installed.
> 
> Setting a 0 length certificate returns the system state to only return
> the host certificates on an extended guest request.
> 
> We also increase the SEV_FW_BLOB_MAX_SIZE another 4K page to allow
> space for an extra certificate.
> 
> Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> 
> Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
> ---
>   arch/x86/kvm/svm/sev.c   | 111 ++++++++++++++++++++++++++++++++++++++-
>   arch/x86/kvm/svm/svm.h   |   1 +
>   include/linux/psp-sev.h  |   2 +-
>   include/uapi/linux/kvm.h |  12 +++++
>   4 files changed, 123 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index a35cd9f33f16..f1d846081213 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1636,6 +1636,7 @@ static void *snp_context_create(struct kvm *kvm, struct kvm_sev_cmd *argp)
>   		goto e_free;
>   
>   	sev->snp_certs_data = certs_data;
> +	sev->snp_certs_len = 0;
>   
>   	return context;
>   
> @@ -1940,6 +1941,86 @@ static int snp_launch_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
>   	return ret;
>   }
>   
> +static int snp_get_instance_certs(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +	struct kvm_sev_snp_get_certs params;
> +
> +	if (!sev_snp_guest(kvm))
> +		return -ENOTTY;
> +
> +	if (!sev->snp_context)
> +		return -EINVAL;
> +
> +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
> +			   sizeof(params)))
> +		return -EFAULT;
> +
> +	/* No instance certs set. */
> +	if (!sev->snp_certs_len)
> +		return -ENOENT;
> +
> +	if (params.certs_len < sev->snp_certs_len) {
> +		/* Output buffer too small. Return the required size. */
> +		params.certs_len = sev->snp_certs_len;
> +
> +		if (copy_to_user((void __user *)(uintptr_t)argp->data, &params,
> +				 sizeof(params)))
> +			return -EFAULT;
> +
> +		return -EINVAL;
> +	}
> +
> +	if (copy_to_user((void __user *)(uintptr_t)params.certs_uaddr,
> +			 sev->snp_certs_data, sev->snp_certs_len))
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
> +static int snp_set_instance_certs(struct kvm *kvm, struct kvm_sev_cmd *argp)
> +{
> +	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +	struct kvm_sev_snp_set_certs params;
> +	void *new_certs = NULL, *to_certs = sev->snp_certs_data;
> +	unsigned long length = SEV_FW_BLOB_MAX_SIZE;
> +
> +	if (!sev_snp_guest(kvm))
> +		return -ENOTTY;
> +
> +	if (!sev->snp_context)
> +		return -EINVAL;
> +
> +	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
> +			   sizeof(params)))
> +		return -EFAULT;
> +
> +	if (params.certs_len > SEV_FW_BLOB_MAX_SIZE)
> +		return -EINVAL;
> +
> +	/*
> +	 * Setting a length of 0 is the same as "uninstalling" instance-
> +	 * specific certificates.
> +	 */
> +	if (params.certs_len == 0) {
> +		sev->snp_certs_len = 0;
> +		return 0;
> +	}
> +
> +	/* Page-align the length */
> +	length = (params.certs_len + PAGE_SIZE - 1) & PAGE_MASK;

Probably can use PAGE_ALIGN() here.

> +
> +	if (copy_from_user(to_certs,
> +			   (void __user *)(uintptr_t)params.certs_uaddr,
> +			   params.certs_len)) {
> +		return -EFAULT;
> +	}
> +
> +	sev->snp_certs_len = length;
> +
> +	return 0;
> +}
> +
>   int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
>   {
>   	struct kvm_sev_cmd sev_cmd;
> @@ -2038,6 +2119,12 @@ int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
>   	case KVM_SEV_SNP_LAUNCH_FINISH:
>   		r = snp_launch_finish(kvm, &sev_cmd);
>   		break;
> +	case KVM_SEV_SNP_GET_CERTS:
> +		r = snp_get_instance_certs(kvm, &sev_cmd);
> +		break;
> +	case KVM_SEV_SNP_SET_CERTS:
> +		r = snp_set_instance_certs(kvm, &sev_cmd);
> +		break;
>   	default:
>   		r = -EINVAL;
>   		goto out;
> @@ -3361,8 +3448,28 @@ static void snp_handle_ext_guest_request(struct vcpu_svm *svm, gpa_t req_gpa, gp
>   	if (rc)
>   		goto unlock;
>   
> -	rc = snp_guest_ext_guest_request(&req, (unsigned long)sev->snp_certs_data,
> -					 &data_npages, &err);
> +	/*
> +	 * If the VMM has overridden the certs, then we change the error message
> +	 * if the size is inappropriate for the override. Otherwise we use a
> +	 * regular guest request and copy back the instance certs.
> +	 */
> +	if (sev->snp_certs_len) {
> +		if ((data_npages << PAGE_SHIFT) < sev->snp_certs_len) {
> +			rc = -EINVAL;
> +			err = SNP_GUEST_REQ_INVALID_LEN;
> +			goto datalen;
> +		}
> +		rc = sev_issue_cmd(kvm, SEV_CMD_SNP_GUEST_REQUEST, &req,
> +				   (int *)&err);
> +	} else {
> +		rc = snp_guest_ext_guest_request(
> +			&req, (unsigned long)sev->snp_certs_data, &data_npages,
> +			&err);
> +	}
> +datalen:
> +	if (sev->snp_certs_len)
> +		data_npages = sev->snp_certs_len >> PAGE_SHIFT;
> +
>   	if (rc) {
>   		/*
>   		 * If buffer length is small then return the expected
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index e68b3aab57d6..9030a295cdf5 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -93,6 +93,7 @@ struct kvm_sev_info {
>   	void *snp_context;      /* SNP guest context page */
>   	struct srcu_struct psc_srcu;
>   	void *snp_certs_data;
> +	unsigned int snp_certs_len; /* Size of instance override for certs */
>   	struct mutex guest_req_lock;
>   
>   	u64 sev_features;	/* Features set at VMSA creation */
> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
> index 859bbbcd5fa3..3d1811ffd9af 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -24,7 +24,7 @@
>   #define __psp_pa(x)	__pa(x)
>   #endif
>   
> -#define SEV_FW_BLOB_MAX_SIZE	0x4000	/* 16KB */
> +#define SEV_FW_BLOB_MAX_SIZE	0x5000	/* 20KB */
>   
>   /**
>    * SEV platform state
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index db9eb36da3ec..d47b36dc681d 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -1717,6 +1717,8 @@ enum sev_cmd_id {
>   	KVM_SEV_SNP_LAUNCH_START,
>   	KVM_SEV_SNP_LAUNCH_UPDATE,
>   	KVM_SEV_SNP_LAUNCH_FINISH,
> +	KVM_SEV_SNP_GET_CERTS,
> +	KVM_SEV_SNP_SET_CERTS,
>   
>   	KVM_SEV_NR_MAX,
>   };
> @@ -1864,6 +1866,16 @@ struct kvm_sev_snp_launch_finish {
>   	__u8 pad[6];
>   };
>   
> +struct kvm_sev_snp_get_certs {
> +	__u64 certs_uaddr;
> +	__u64 certs_len;
> +};
> +
> +struct kvm_sev_snp_set_certs {
> +	__u64 certs_uaddr;
> +	__u64 certs_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)
> 

Otherwise, patch looks good to me.

Reviewed-by: Ashish Kalra <ashish.kalra@amd.com>

Thanks,
Ashish