On Tue, Sep 01, 2026 at 12:09:18PM +0200, Luigi Leonardi 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.
IIUC the behaviour is the same after this patch, but IMO better to
clarify.
Signed-off-by: Luigi Leonardi <[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,
I'm confused, this commit says "rename set_guest_policy to set_id_block"
so why this callback is still here?
- 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
