> On 1 Sep 2026, at 3:39 PM, Luigi Leonardi <[email protected]> wrote:
>
> The guest policy must be provided at guest launch start: LAUNCH_START for
> SEV/SEV-ES and SNP_LAUNCH_START for SEV-SNP. See the SEV API
> specification, chapter 3 (Guest Policy), and the SEV-SNP firmware ABI
> specification, section 4.3 (Guest Policy).
>
> The policy parameter in set_guest_policy was never effective: by the
> time this callback runs, LAUNCH_START has already been issued for both
> SEV/SEV-ES and SEV-SNP, so writing to kvm_start_conf.policy or
> sev_guest->policy has no effect. In practice the only thing this
> callback actually does is set the ID block and ID auth for SNP's
> LAUNCH_FINISH, so rename it to set_id_block to reflect its real
> purpose, remove the unused policy parameter, and drop the non-SNP code
> path which was entirely dead.
>
> This is preliminary work: actually forwarding the guest policy to the
> platform before LAUNCH_START is added in a later commit.
>
> Signed-off-by: Luigi Leonardi <[email protected]>
Reviewed-by: Ani Sinha <[email protected]>
> ---
> backends/confidential-guest-support.c | 12 ++-
> backends/igvm.c | 6 +-
> include/system/confidential-guest-support.h | 28 ++++---
> target/i386/sev.c | 118 +++++++++++-----------------
> 4 files changed, 67 insertions(+), 97 deletions(-)
>
> diff --git a/backends/confidential-guest-support.c
> b/backends/confidential-guest-support.c
> index 156dd15e66..a0b36d2da5 100644
> --- a/backends/confidential-guest-support.c
> +++ b/backends/confidential-guest-support.c
> @@ -38,14 +38,12 @@ static int set_guest_state(hwaddr gpa, uint8_t *ptr,
> uint64_t len,
> return -1;
> }
>
> -static int set_guest_policy(ConfidentialGuestPolicyType policy_type,
> - uint64_t policy,
> - void *policy_data1, uint32_t policy_data1_size,
> - void *policy_data2, uint32_t policy_data2_size,
> - Error **errp)
> +static int set_id_block(void *id_block, uint32_t id_block_size,
> + void *id_auth, uint32_t id_auth_size,
> + Error **errp)
> {
> error_setg(errp,
> - "Setting confidential guest policy is not supported for this
> platform");
> + "Setting ID block is not supported for this platform");
> return -1;
> }
>
> @@ -64,7 +62,7 @@ static void
> confidential_guest_support_class_init(ObjectClass *oc,
> ConfidentialGuestSupportClass *cgsc =
> CONFIDENTIAL_GUEST_SUPPORT_CLASS(oc);
> cgsc->check_support = check_support;
> cgsc->set_guest_state = set_guest_state;
> - cgsc->set_guest_policy = set_guest_policy;
> + cgsc->set_id_block = set_id_block;
> cgsc->get_mem_map_entry = get_mem_map_entry;
> }
>
> diff --git a/backends/igvm.c b/backends/igvm.c
> index 7b7bdc72b7..85de0d54ec 100644
> --- a/backends/igvm.c
> +++ b/backends/igvm.c
> @@ -968,9 +968,9 @@ static int qigvm_handle_policy(QIgvm *ctx, Error **errp)
> id_block_len = sizeof(struct sev_id_block);
> id_auth_len = sizeof(struct sev_id_authentication);
> }
> - return ctx->cgsc->set_guest_policy(GUEST_POLICY_SEV, ctx->sev_policy,
> - ctx->id_block, id_block_len,
> - ctx->id_auth, id_auth_len, errp);
> +
> + return ctx->cgsc->set_id_block(ctx->id_block, id_block_len,
> + ctx->id_auth, id_auth_len, errp);
> }
> return 0;
> }
> diff --git a/include/system/confidential-guest-support.h
> b/include/system/confidential-guest-support.h
> index 5dca717308..6d35ddb97a 100644
> --- a/include/system/confidential-guest-support.h
> +++ b/include/system/confidential-guest-support.h
> @@ -128,21 +128,23 @@ typedef struct ConfidentialGuestSupportClass {
> uint16_t cpu_index, Error **errp);
>
> /*
> - * Set the guest policy. The policy can be used to configure the
> - * confidential platform, such as if debug is enabled or not and can
> contain
> - * information about expected launch measurements, signed verification of
> - * guest configuration and other platform data.
> - *
> - * The format of the policy data is specific to each platform. For
> example,
> - * SEV-SNP uses a policy bitfield in the 'policy' argument and provides
> an
> - * ID block and ID authentication in the 'policy_data' parameters. The
> type
> - * of policy data is identified by the 'policy_type' argument.
> + * Set the guest policy for the confidential platform. The policy
> + * configures properties of the guest, such as whether debug is
> + * enabled. Its format is platform-specific; for SEV/SEV-ES and
> + * SEV-SNP it is a policy bitfield. Must be called before LAUNCH_START
> + * so the policy is in effect for launch.
> */
> int (*set_guest_policy)(ConfidentialGuestPolicyType policy_type,
> - uint64_t policy,
> - void *policy_data1, uint32_t policy_data1_size,
> - void *policy_data2, uint32_t policy_data2_size,
> - Error **errp);
> + uint64_t policy, Error **errp);
> +
> + /*
> + * Set the SEV-SNP ID block and ID authentication block. These are
> + * passed to SNP_LAUNCH_FINISH to provide signed verification of the
> + * guest configuration.
> + */
> + int (*set_id_block)(void *id_block, uint32_t id_block_size,
> + void *id_auth, uint32_t id_auth_size,
> + Error **errp);
>
> /*
> * Iterate the system memory map, getting the entry with the given index
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index 4d875d10ff..465415c535 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -2723,10 +2723,9 @@ static int cgs_get_mem_map_entry(int index,
> return 0;
> }
>
> -static int cgs_set_guest_policy(ConfidentialGuestPolicyType policy_type,
> - uint64_t policy, void *policy_data1,
> - uint32_t policy_data1_size, void
> *policy_data2,
> - uint32_t policy_data2_size, Error **errp)
> +static int cgs_set_id_block(void *id_block, uint32_t id_block_size,
> + void *id_auth, uint32_t id_auth_size,
> + Error **errp)
> {
> SevCommonState *sev_common = SEV_COMMON(MACHINE(qdev_get_machine())->cgs);
> if (sev_common->state == SEV_STATE_UNINIT) {
> @@ -2734,86 +2733,57 @@ static int
> cgs_set_guest_policy(ConfidentialGuestPolicyType policy_type,
> return 0;
> }
>
> - if (policy_type != GUEST_POLICY_SEV) {
> - error_setg(errp, "SEV: Invalid guest policy type provided for SEV:
> %d",
> - policy_type);
> + if (!sev_snp_enabled()) {
> + error_setg(errp, "SEV: ID block is only supported for SEV-SNP");
> return -1;
> }
> - /*
> - * SEV-SNP handles policy differently. The policy flags are defined in
> - * kvm_start_conf.policy and an ID block and ID auth can be provided.
> - */
> - if (sev_snp_enabled()) {
> - SevSnpGuestState *sev_snp_guest =
> - SEV_SNP_GUEST(MACHINE(qdev_get_machine())->cgs);
> - struct kvm_sev_snp_launch_finish *finish =
> - &sev_snp_guest->kvm_finish_conf;
>
> - /*
> - * The policy consists of flags in 'policy' and optionally an ID
> block
> - * and ID auth in policy_data1 and policy_data2 respectively. The ID
> - * block and auth are optional so clear any previous ID block and
> auth
> - * and set them if provided, but always set the policy flags.
> - */
> - g_free(sev_snp_guest->id_block);
> - g_free((guchar *)finish->id_block_uaddr);
> - g_free(sev_snp_guest->id_auth);
> - g_free((guchar *)finish->id_auth_uaddr);
> - sev_snp_guest->id_block = NULL;
> - finish->id_block_uaddr = 0;
> - sev_snp_guest->id_auth = NULL;
> - finish->id_auth_uaddr = 0;
> -
> - if (policy_data1_size > 0) {
> - struct sev_snp_id_authentication *id_auth =
> - (struct sev_snp_id_authentication *)policy_data2;
> -
> - if (policy_data1_size != KVM_SEV_SNP_ID_BLOCK_SIZE) {
> - error_setg(errp, "SEV: Invalid SEV-SNP ID block: incorrect
> size");
> - return -1;
> - }
> - if (policy_data2_size != KVM_SEV_SNP_ID_AUTH_SIZE) {
> - error_setg(errp,
> - "SEV: Invalid SEV-SNP ID auth block: incorrect
> size");
> - return -1;
> - }
> - assert(policy_data1 != NULL);
> - assert(policy_data2 != NULL);
> + SevSnpGuestState *sev_snp_guest =
> + SEV_SNP_GUEST(MACHINE(qdev_get_machine())->cgs);
> + struct kvm_sev_snp_launch_finish *finish =
> + &sev_snp_guest->kvm_finish_conf;
>
> - finish->id_block_uaddr =
> - (__u64)g_memdup2(policy_data1, KVM_SEV_SNP_ID_BLOCK_SIZE);
> - finish->id_auth_uaddr =
> - (__u64)g_memdup2(policy_data2, KVM_SEV_SNP_ID_AUTH_SIZE);
> + g_free(sev_snp_guest->id_block);
> + g_free((guchar *)finish->id_block_uaddr);
> + g_free(sev_snp_guest->id_auth);
> + g_free((guchar *)finish->id_auth_uaddr);
> + sev_snp_guest->id_block = NULL;
> + finish->id_block_uaddr = 0;
> + sev_snp_guest->id_auth = NULL;
> + finish->id_auth_uaddr = 0;
>
> - /*
> - * Check if an author key has been provided and use that to flag
> - * whether the author key is enabled. The first of the author key
> - * must be non-zero to indicate the key type, which will
> currently
> - * always be 2.
> - */
> - sev_snp_guest->kvm_finish_conf.auth_key_en =
> - id_auth->author_key[0] ? 1 : 0;
> - finish->id_block_en = 1;
> - }
> + if (id_block_size > 0) {
> + struct sev_snp_id_authentication *auth =
> + (struct sev_snp_id_authentication *)id_auth;
>
> - /* do not reset existing policy if policy was not set in IGVM */
> - if (policy != 0) {
> - sev_snp_guest->kvm_start_conf.policy = policy;
> + if (id_block_size != KVM_SEV_SNP_ID_BLOCK_SIZE) {
> + error_setg(errp, "SEV: Invalid SEV-SNP ID block: incorrect
> size");
> + return -1;
> }
> - } else {
> - SevGuestState *sev_guest =
> SEV_GUEST(MACHINE(qdev_get_machine())->cgs);
> - /* Only the policy flags are supported for SEV and SEV-ES */
> - if ((policy_data1_size > 0) || (policy_data2_size > 0) ||
> !sev_guest) {
> - error_setg(errp, "SEV: An ID block/ID auth block has been
> provided "
> - "but SEV-SNP is not enabled");
> + if (id_auth_size != KVM_SEV_SNP_ID_AUTH_SIZE) {
> + error_setg(errp,
> + "SEV: Invalid SEV-SNP ID auth block: incorrect size");
> return -1;
> }
> + assert(id_block != NULL);
> + assert(id_auth != NULL);
>
> - /* do not reset existing policy if policy was not set in IGVM */
> - if (policy != 0) {
> - sev_guest->policy = policy;
> - }
> + finish->id_block_uaddr =
> + (__u64)g_memdup2(id_block, KVM_SEV_SNP_ID_BLOCK_SIZE);
> + finish->id_auth_uaddr =
> + (__u64)g_memdup2(id_auth, KVM_SEV_SNP_ID_AUTH_SIZE);
> +
> + /*
> + * Check if an author key has been provided and use that to flag
> + * whether the author key is enabled. The first of the author key
> + * must be non-zero to indicate the key type, which will currently
> + * always be 2.
> + */
> + sev_snp_guest->kvm_finish_conf.auth_key_en =
> + auth->author_key[0] ? 1 : 0;
> + finish->id_block_en = 1;
> }
> +
> return 0;
> }
>
> @@ -2878,7 +2848,7 @@ sev_common_instance_init(Object *obj)
> cgs->check_support = cgs_check_support;
> cgs->set_guest_state = cgs_set_guest_state;
> cgs->get_mem_map_entry = cgs_get_mem_map_entry;
> - cgs->set_guest_policy = cgs_set_guest_policy;
> + cgs->set_id_block = cgs_set_id_block;
> cgs->can_rebuild_guest_state = true;
>
> QTAILQ_INIT(&sev_common->launch_vmsa);
>
> --
> 2.55.0
>
