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Date: Wed, 12 Oct 2022 18:39:14 -0500
From: "Kalra, Ashish" <ashish.kalra@....com>
To: Dionna Glaze <dionnaglaze@...gle.com>,
linux-kernel@...r.kernel.org, x86@...nel.org
Cc: Tom Lendacky <Thomas.Lendacky@....com>,
Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 1/2] x86/sev: Add KVM commands for instance certs
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@....com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
>
> Signed-off-by: Dionna Glaze <dionnaglaze@...gle.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(¶ms, (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, ¶ms,
> + 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(¶ms, (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@....com>
Thanks,
Ashish
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