> On 1 Sep 2026, at 3:39 PM, Luigi Leonardi <[email protected]> wrote:
>
> The guest policy carried in the IGVM guest-policy initialization header
> was parsed into QIgvm but never forwarded to the confidential guest
> platform: the previous callback ran at the end of qigvm_process_file,
> after LAUNCH_START had already been issued, so writing the policy had
> no effect.
>
> Add a set_guest_policy callback and invoke it from the guest-policy
> initialization handler, so the policy reaches the platform before
> LAUNCH_START.
>
> The guest policy can also be set on the command line. As it is part of
> the attestation report, silently overriding it would cause attestation
> to fail, so return an error if the command-line value differs from the
> one supplied by the IGVM file.
>
> Link: https://gitlab.com/qemu-project/qemu/-/work_items/4189
> Fixes: 915b47078d ("backends/igvm: Handle policy for SEV guests")
> Signed-off-by: Luigi Leonardi <[email protected]>
> ---
> backends/confidential-guest-support.c | 9 ++++++++
> backends/igvm.c | 4 ++++
> target/i386/sev.c | 39 +++++++++++++++++++++++++++++++++++
> 3 files changed, 52 insertions(+)
>
> diff --git a/backends/confidential-guest-support.c
> b/backends/confidential-guest-support.c
> index a0b36d2da5..c0d15b4a76 100644
> --- a/backends/confidential-guest-support.c
> +++ b/backends/confidential-guest-support.c
> @@ -38,6 +38,14 @@ 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, Error **errp)
> +{
> + error_setg(errp,
> + "Setting 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)
> @@ -62,6 +70,7 @@ 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 6545382546..5131ee7829 100644
> --- a/backends/igvm.c
> +++ b/backends/igvm.c
> @@ -868,6 +868,10 @@ static int qigvm_initialization_guest_policy(QIgvm *ctx,
>
> if (guest->compatibility_mask & ctx->compatibility_mask) {
> ctx->sev_policy = guest->policy;
> + if (ctx->cgsc) {
> + return ctx->cgsc->set_guest_policy(GUEST_POLICY_SEV,
> + guest->policy, errp);
> + }
> }
> return 0;
> }
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index c76cdba8d2..533ea4b54e 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -128,6 +128,8 @@ struct SevCommonState {
> bool kernel_hashes;
> uint64_t sev_features;
> uint64_t supported_sev_features;
> + /* whether the guest policy was explicitly set on the command line */
> + bool policy_set;
>
> /* runtime state */
> uint8_t api_major;
> @@ -2723,6 +2725,40 @@ static int cgs_get_mem_map_entry(int index,
> return 0;
> }
>
> +static int cgs_set_guest_policy(ConfidentialGuestPolicyType policy_type,
> + uint64_t policy, Error **errp)
> +{
> + SevCommonState *sev_common =
> SEV_COMMON(MACHINE(qdev_get_machine())->cgs);
> +
> + if (policy_type != GUEST_POLICY_SEV) {
> + error_setg(errp, "SEV: Invalid guest policy type provided for SEV:
> %d",
> + policy_type);
> + return -1;
> + }
> +
> + if (sev_snp_enabled()) {
> + SevSnpGuestState *sev_snp_guest = SEV_SNP_GUEST(sev_common);
> +
> + if (sev_common->policy_set &&
> + sev_snp_guest->kvm_start_conf.policy != policy) {
> + error_setg(errp, "SNP: policy mismatch between IGVM and CLI");
> + return -1;
> + }
> +
> + sev_snp_guest->kvm_start_conf.policy = policy;
I had fixed a bug initially here where we need to check if the policy passed is
not 0. I am not sure if that fix is still needed here.
Please test this scenario:
a) Generate an IGVM file with policy set to 0.
b) Start a confidential SEV-SNP guest with policy set in command line and with
this IGVM.
I think with your patch this will fail as the policies won’t match. This
potentially breaks some tests. For example, with your patch, does my FUKI
confidential tests still pass?
c) If b) works, reset the guest and check if the guest is still a SEV-SNP guest.
> + } else {
> + SevGuestState *sev_guest = SEV_GUEST(sev_common);
> +
> + if (sev_common->policy_set && sev_guest->policy != policy) {
> + error_setg(errp, "SEV: policy mismatch between IGVM and CLI");
> + return -1;
> + }
> +
> + sev_guest->policy = policy;
> + }
> + return 0;
> +}
> +
> static int cgs_set_id_block(void *id_block, uint32_t id_block_size,
> void *id_auth, uint32_t id_auth_size,
> Error **errp)
> @@ -2848,6 +2884,7 @@ 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;
>
> @@ -2970,6 +3007,7 @@ sev_guest_set_policy(Object *obj, Visitor *v, const
> char *name,
> if (!visit_type_uint32(v, name, &SEV_GUEST(obj)->policy, errp)) {
> return;
> }
> + SEV_COMMON(obj)->policy_set = true;
> }
>
> static void
> @@ -3027,6 +3065,7 @@ sev_snp_guest_set_policy(Object *obj, Visitor *v, const
> char *name,
> errp)) {
> return;
> }
> + SEV_COMMON(obj)->policy_set = true;
> }
>
> static char *
>
> --
> 2.55.0
>
