Re: [PATCH v2 1/5] sev: split set_guest_policy into set_guest_policy and set_id_block

[Ani Sinha <anisinha@redhat.com>]

> On 7 Sep 2026, at 9:26 PM, Luigi Leonardi <leonardi@redhat.com> wrote:
> 
> The set_guest_policy callback on ConfidentialGuestSupportClass mixed
> two unrelated jobs: writing the guest policy bits and providing the
> SEV-SNP ID block/ID auth for LAUNCH_FINISH. The two are only related
> because both come from the same 'policy' section of the SEV/SEV-SNP
> launch flow, but they need to be set at different times: the policy
> must be in effect before LAUNCH_START, while the ID block is only
> needed before LAUNCH_FINISH.
> 
> Split the combined callback into set_guest_policy(policy_type, policy,
> errp) and set_id_block(id_block, id_block_size, id_auth, id_auth_size,
> errp), keeping both call sites exactly where the combined callback used
> to be called from. No functional change.

LGTM.

Reviewed-by: Ani Sinha <anisinha@redhat.com>

> 
> Signed-off-by: Luigi Leonardi <leonardi@redhat.com>
> ---
> backends/confidential-guest-support.c       |  15 ++-
> backends/igvm.c                             |  14 ++-
> include/system/confidential-guest-support.h |  28 +++---
> target/i386/sev.c                           | 140 +++++++++++++++-------------
> 4 files changed, 111 insertions(+), 86 deletions(-)
> 
> diff --git a/backends/confidential-guest-support.c b/backends/confidential-guest-support.c
> index 156dd15e66..d60d1f6eaa 100644
> --- a/backends/confidential-guest-support.c
> +++ b/backends/confidential-guest-support.c
> @@ -39,16 +39,22 @@ static int set_guest_state(hwaddr gpa, uint8_t *ptr, uint64_t len,
> }
> 
> 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)
> +                            uint64_t policy, Error **errp)
> {
>     error_setg(errp,
>                "Setting confidential guest policy is not supported for this platform");
>     return -1;
> }
> 
> +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 ID block is not supported for this platform");
> +    return -1;
> +}
> +
> static int get_mem_map_entry(int index, ConfidentialGuestMemoryMapEntry *entry,
>                              Error **errp)
> {
> @@ -65,6 +71,7 @@ static void confidential_guest_support_class_init(ObjectClass *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..99304d6467 100644
> --- a/backends/igvm.c
> +++ b/backends/igvm.c
> @@ -963,14 +963,22 @@ static int qigvm_handle_policy(QIgvm *ctx, Error **errp)
>     if (ctx->platform_type == IGVM_PLATFORM_TYPE_SEV_SNP) {
>         int id_block_len = 0;
>         int id_auth_len = 0;
> +        int retval;
> +
>         if (ctx->id_block) {
>             ctx->id_block->policy = ctx->sev_policy;
>             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);
> +
> +        retval = ctx->cgsc->set_guest_policy(GUEST_POLICY_SEV, ctx->sev_policy,
> +                                             errp);
> +        if (retval < 0) {
> +            return retval;
> +        }
> +
> +        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 cc16c6b071..b53d13e2fa 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -2726,9 +2726,7 @@ static int cgs_get_mem_map_entry(int index,
> }
> 
> 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)
> +                                uint64_t policy, Error **errp)
> {
>     SevCommonState *sev_common = SEV_COMMON(MACHINE(qdev_get_machine())->cgs);
>     if (sev_common->state == SEV_STATE_UNINIT) {
> @@ -2741,81 +2739,90 @@ static int cgs_set_guest_policy(ConfidentialGuestPolicyType policy_type,
>                    policy_type);
>         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.
> -     */
> +
> +    /* do not reset existing policy if policy was not set in IGVM  */
> +    if (policy == 0) {
> +        return 0;
> +    }
> +
>     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);
> +        sev_snp_guest->kvm_start_conf.policy = policy;
> +    } else {
> +        SevGuestState *sev_guest = SEV_GUEST(MACHINE(qdev_get_machine())->cgs);
> 
> -            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);
> +        sev_guest->policy = policy;
> +    }
> +    return 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;
> -        }
> +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) {
> +        /* Pre-processing of IGVM file called from sev_common_kvm_init() */
> +        return 0;
> +    }
> +
> +    if (!sev_snp_enabled()) {
> +        error_setg(errp, "SEV: ID block is only supported for SEV-SNP");
> +        return -1;
> +    }
> 
> -        /* do not reset existing policy if policy was not set in IGVM  */
> -        if (policy != 0) {
> -            sev_snp_guest->kvm_start_conf.policy = policy;
> +    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;
> +
> +    /*
> +     * Drop any ID block and ID auth from a previous pass before repopulating
> +     * them, then set them only if an ID block was provided.
> +     */
> +    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 (id_block_size > 0) {
> +        struct sev_snp_id_authentication *auth =
> +            (struct sev_snp_id_authentication *)id_auth;
> +
> +        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;
> }
> 
> @@ -2881,6 +2888,7 @@ sev_common_instance_init(Object *obj)
>     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
>