From 2872c423fa44dcbf50b581a5c3feac064a0473a0 Mon Sep 17 00:00:00 2001 From: Michael Roth Date: Tue, 9 Apr 2024 18:07:41 -0500 Subject: [PATCH 024/100] i386/sev: Add 'legacy-vm-type' parameter for SEV guest objects RH-Author: Paolo Bonzini RH-MergeRequest: 245: SEV-SNP support RH-Jira: RHEL-39544 RH-Acked-by: Thomas Huth RH-Acked-by: Bandan Das RH-Acked-by: Vitaly Kuznetsov RH-Commit: [24/91] ce35d1b09fe8aa8772ff149543f7760455c1e6b5 (bonzini/rhel-qemu-kvm) QEMU will currently automatically make use of the KVM_SEV_INIT2 API for initializing SEV and SEV-ES guests verses the older KVM_SEV_INIT/KVM_SEV_ES_INIT interfaces. However, the older interfaces will silently avoid sync'ing FPU/XSAVE state to the VMSA prior to encryption, thus relying on behavior and measurements that assume the related fields to be allow zero. With KVM_SEV_INIT2, this state is now synced into the VMSA, resulting in measurements changes and, theoretically, behaviorial changes, though the latter are unlikely to be seen in practice. To allow a smooth transition to the newer interface, while still providing a mechanism to maintain backward compatibility with VMs created using the older interfaces, provide a new command-line parameter: -object sev-guest,legacy-vm-type=true,... and have it default to false. Signed-off-by: Michael Roth Message-ID: <20240409230743.962513-2-michael.roth@amd.com> Signed-off-by: Paolo Bonzini (cherry picked from commit 023267334da375226720e62963df9545aa8fc2fd) Signed-off-by: Paolo Bonzini --- qapi/qom.json | 11 ++++++++++- target/i386/sev.c | 18 +++++++++++++++++- 2 files changed, 27 insertions(+), 2 deletions(-) diff --git a/qapi/qom.json b/qapi/qom.json index 85e6b4f84a..38dde6d785 100644 --- a/qapi/qom.json +++ b/qapi/qom.json @@ -898,6 +898,14 @@ # designated guest firmware page for measured boot with -kernel # (default: false) (since 6.2) # +# @legacy-vm-type: Use legacy KVM_SEV_INIT KVM interface for creating the VM. +# The newer KVM_SEV_INIT2 interface syncs additional vCPU +# state when initializing the VMSA structures, which will +# result in a different guest measurement. Set this to +# maintain compatibility with older QEMU or kernel versions +# that rely on legacy KVM_SEV_INIT behavior. +# (default: false) (since 9.1) +# # Since: 2.12 ## { 'struct': 'SevGuestProperties', @@ -908,7 +916,8 @@ '*handle': 'uint32', '*cbitpos': 'uint32', 'reduced-phys-bits': 'uint32', - '*kernel-hashes': 'bool' } } + '*kernel-hashes': 'bool', + '*legacy-vm-type': 'bool' } } ## # @ThreadContextProperties: diff --git a/target/i386/sev.c b/target/i386/sev.c index 9dab4060b8..f4ee317cb0 100644 --- a/target/i386/sev.c +++ b/target/i386/sev.c @@ -67,6 +67,7 @@ struct SevGuestState { uint32_t cbitpos; uint32_t reduced_phys_bits; bool kernel_hashes; + bool legacy_vm_type; /* runtime state */ uint32_t handle; @@ -356,6 +357,16 @@ static void sev_guest_set_kernel_hashes(Object *obj, bool value, Error **errp) sev->kernel_hashes = value; } +static bool sev_guest_get_legacy_vm_type(Object *obj, Error **errp) +{ + return SEV_GUEST(obj)->legacy_vm_type; +} + +static void sev_guest_set_legacy_vm_type(Object *obj, bool value, Error **errp) +{ + SEV_GUEST(obj)->legacy_vm_type = value; +} + bool sev_enabled(void) { @@ -863,7 +874,7 @@ static int sev_kvm_type(X86ConfidentialGuest *cg) } kvm_type = (sev->policy & SEV_POLICY_ES) ? KVM_X86_SEV_ES_VM : KVM_X86_SEV_VM; - if (kvm_is_vm_type_supported(kvm_type)) { + if (kvm_is_vm_type_supported(kvm_type) && !sev->legacy_vm_type) { sev->kvm_type = kvm_type; } else { sev->kvm_type = KVM_X86_DEFAULT_VM; @@ -1381,6 +1392,11 @@ sev_guest_class_init(ObjectClass *oc, void *data) sev_guest_set_kernel_hashes); object_class_property_set_description(oc, "kernel-hashes", "add kernel hashes to guest firmware for measured Linux boot"); + object_class_property_add_bool(oc, "legacy-vm-type", + sev_guest_get_legacy_vm_type, + sev_guest_set_legacy_vm_type); + object_class_property_set_description(oc, "legacy-vm-type", + "use legacy VM type to maintain measurement compatibility with older QEMU or kernel versions."); } static void -- 2.39.3