On Tue, May 24, 2022 at 10:03:02PM +0800, Chenyi Qiang wrote:
> There are cases that malicious virtual machine can cause CPU stuck (due
> to event windows don't open up), e.g., infinite loop in microcode when
> nested #AC (CVE-2015-5307). No event window means no event (NMI, SMI and
> IRQ) can be delivered. It leads the CPU to be unavailable to host or
> other VMs. Notify VM exit is introduced to mitigate such kind of
> attacks, which will generate a VM exit if no event window occurs in VM
> non-root mode for a specified amount of time (notify window).
>
> A new KVM capability KVM_CAP_X86_NOTIFY_VMEXIT is exposed to user space
> so that the user can query the capability and set the expected notify
> window when creating VMs. The format of the argument when enabling this
> capability is as follows:
> Bit 63:32 - notify window specified in qemu command
> Bit 31:0 - some flags (e.g. KVM_X86_NOTIFY_VMEXIT_ENABLED is set to
> enable the feature.)
>
> Because there are some concerns, e.g. a notify VM exit may happen with
> VM_CONTEXT_INVALID set in exit qualification (no cases are anticipated
> that would set this bit), which means VM context is corrupted. To avoid
> the false positive and a well-behaved guest gets killed, make this
> feature disabled by default. Users can enable the feature by a new
> machine property:
> qemu -machine notify_vmexit=on,notify_window=0 ...
>
> A new KVM exit reason KVM_EXIT_NOTIFY is defined for notify VM exit. If
> it happens with VM_INVALID_CONTEXT, hypervisor exits to user space to
> inform the fatal case. Then user space can inject a SHUTDOWN event to
> the target vcpu. This is implemented by injecting a sythesized triple
> fault event.
>
> Signed-off-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx>
> ---
> hw/i386/x86.c | 45 +++++++++++++++++++++++++++++
> include/hw/i386/x86.h | 5 ++++
> target/i386/kvm/kvm.c | 66 ++++++++++++++++++++++++++++++-------------
> 3 files changed, 96 insertions(+), 20 deletions(-)
>
> diff --git a/hw/i386/x86.c b/hw/i386/x86.c
> index 4cf107baea..a82f959cb9 100644
> --- a/hw/i386/x86.c
> +++ b/hw/i386/x86.c
> @@ -1296,6 +1296,37 @@ static void machine_set_sgx_epc(Object *obj, Visitor *v, const char *name,
> qapi_free_SgxEPCList(list);
> }
>
> +static bool x86_machine_get_notify_vmexit(Object *obj, Error **errp)
> +{
> + X86MachineState *x86ms = X86_MACHINE(obj);
> +
> + return x86ms->notify_vmexit;
> +}
> +
> +static void x86_machine_set_notify_vmexit(Object *obj, bool value, Error **errp)
> +{
> + X86MachineState *x86ms = X86_MACHINE(obj);
> +
> + x86ms->notify_vmexit = value;
> +}
> +
> +static void x86_machine_get_notify_window(Object *obj, Visitor *v,
> + const char *name, void *opaque, Error **errp)
> +{
> + X86MachineState *x86ms = X86_MACHINE(obj);
> + uint32_t notify_window = x86ms->notify_window;
> +
> + visit_type_uint32(v, name, ¬ify_window, errp);
> +}
> +
> +static void x86_machine_set_notify_window(Object *obj, Visitor *v,
> + const char *name, void *opaque, Error **errp)
> +{
> + X86MachineState *x86ms = X86_MACHINE(obj);
> +
> + visit_type_uint32(v, name, &x86ms->notify_window, errp);
> +}
> +
> static void x86_machine_initfn(Object *obj)
> {
> X86MachineState *x86ms = X86_MACHINE(obj);
> @@ -1306,6 +1337,8 @@ static void x86_machine_initfn(Object *obj)
> x86ms->oem_id = g_strndup(ACPI_BUILD_APPNAME6, 6);
> x86ms->oem_table_id = g_strndup(ACPI_BUILD_APPNAME8, 8);
> x86ms->bus_lock_ratelimit = 0;
> + x86ms->notify_vmexit = false;
> + x86ms->notify_window = 0;
> }
>
> static void x86_machine_class_init(ObjectClass *oc, void *data)
> @@ -1361,6 +1394,18 @@ static void x86_machine_class_init(ObjectClass *oc, void *data)
> NULL, NULL);
> object_class_property_set_description(oc, "sgx-epc",
> "SGX EPC device");
> +
> + object_class_property_add(oc, X86_MACHINE_NOTIFY_WINDOW, "uint32_t",
> + x86_machine_get_notify_window,
> + x86_machine_set_notify_window, NULL, NULL);
> + object_class_property_set_description(oc, X86_MACHINE_NOTIFY_WINDOW,
> + "Set the notify window required by notify VM exit");
> +
> + object_class_property_add_bool(oc, X86_MACHINE_NOTIFY_VMEXIT,
> + x86_machine_get_notify_vmexit,
> + x86_machine_set_notify_vmexit);
> + object_class_property_set_description(oc, X86_MACHINE_NOTIFY_VMEXIT,
> + "Enable notify VM exit");
> }
>
> static const TypeInfo x86_machine_info = {
> diff --git a/include/hw/i386/x86.h b/include/hw/i386/x86.h
> index 916cc325ee..571ee8b667 100644
> --- a/include/hw/i386/x86.h
> +++ b/include/hw/i386/x86.h
> @@ -80,6 +80,9 @@ struct X86MachineState {
> * which means no limitation on the guest's bus locks.
> */
> uint64_t bus_lock_ratelimit;
> +
> + bool notify_vmexit;
> + uint32_t notify_window;
> };
>
> #define X86_MACHINE_SMM "smm"
> @@ -87,6 +90,8 @@ struct X86MachineState {
> #define X86_MACHINE_OEM_ID "x-oem-id"
> #define X86_MACHINE_OEM_TABLE_ID "x-oem-table-id"
> #define X86_MACHINE_BUS_LOCK_RATELIMIT "bus-lock-ratelimit"
> +#define X86_MACHINE_NOTIFY_VMEXIT "notify-vmexit"
> +#define X86_MACHINE_NOTIFY_WINDOW "notify-window"
>
> #define TYPE_X86_MACHINE MACHINE_TYPE_NAME("x86")
> OBJECT_DECLARE_TYPE(X86MachineState, X86MachineClass, X86_MACHINE)
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index 2f2fc18b4f..6aaedf3412 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -2345,6 +2345,10 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> int ret;
> struct utsname utsname;
> Error *local_err = NULL;
> + X86MachineState *x86ms;
> +
> + assert(object_dynamic_cast(OBJECT(ms), TYPE_X86_MACHINE));
> + x86ms = X86_MACHINE(ms);
>
> /*
> * Initialize SEV context, if required
> @@ -2450,8 +2454,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> }
>
> if (kvm_check_extension(s, KVM_CAP_X86_SMM) &&
> - object_dynamic_cast(OBJECT(ms), TYPE_X86_MACHINE) &&
> - x86_machine_is_smm_enabled(X86_MACHINE(ms))) {
> + x86_machine_is_smm_enabled(x86ms)) {
> smram_machine_done.notify = register_smram_listener;
> qemu_add_machine_init_done_notifier(&smram_machine_done);
> }
> @@ -2479,25 +2482,34 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> }
> }
>
> - if (object_dynamic_cast(OBJECT(ms), TYPE_X86_MACHINE)) {
The original behavior:
if (object_dynamic_cast(OBJECT(ms), TYPE_X86_MACHINE)) {
... do some thing }
return 0;
Note that it won't throw any exceptions if ms is not
instance of TYPE_X86_MACHINE, but now the assert() throws
exceptions in this case. In another hand, assert() may
become nothing in NDEBUG case.
May move the whole BUS LOCK part and new NOTIFY_VMEXIT part
to 2 separate functions and call them from kvm_arch_init()
makes the readability better.
> - X86MachineState *x86ms = X86_MACHINE(ms);
> + if (x86ms->bus_lock_ratelimit > 0) {
> + ret = kvm_check_extension(s, KVM_CAP_X86_BUS_LOCK_EXIT);
> + if (!(ret & KVM_BUS_LOCK_DETECTION_EXIT)) {
> + error_report("kvm: bus lock detection unsupported");
> + return -ENOTSUP;
> + }
> + ret = kvm_vm_enable_cap(s, KVM_CAP_X86_BUS_LOCK_EXIT, 0,
> + KVM_BUS_LOCK_DETECTION_EXIT);
> + if (ret < 0) {
> + error_report("kvm: Failed to enable bus lock detection cap: %s",
> + strerror(-ret));
> + return ret;
> + }
> + ratelimit_init(&bus_lock_ratelimit_ctrl);
> + ratelimit_set_speed(&bus_lock_ratelimit_ctrl,
> + x86ms->bus_lock_ratelimit, BUS_LOCK_SLICE_TIME);
> + }
>
> - if (x86ms->bus_lock_ratelimit > 0) {
> - ret = kvm_check_extension(s, KVM_CAP_X86_BUS_LOCK_EXIT);
> - if (!(ret & KVM_BUS_LOCK_DETECTION_EXIT)) {
> - error_report("kvm: bus lock detection unsupported");
> - return -ENOTSUP;
> - }
> - ret = kvm_vm_enable_cap(s, KVM_CAP_X86_BUS_LOCK_EXIT, 0,
> - KVM_BUS_LOCK_DETECTION_EXIT);
> - if (ret < 0) {
> - error_report("kvm: Failed to enable bus lock detection cap: %s",
> - strerror(-ret));
> - return ret;
> - }
> - ratelimit_init(&bus_lock_ratelimit_ctrl);
> - ratelimit_set_speed(&bus_lock_ratelimit_ctrl,
> - x86ms->bus_lock_ratelimit, BUS_LOCK_SLICE_TIME);
> + if (x86ms->notify_vmexit && kvm_check_extension(s, KVM_CAP_X86_NOTIFY_VMEXIT)) {
> + uint64_t notify_window_flags = ((uint64_t)x86ms->notify_window << 32) |
> + KVM_X86_NOTIFY_VMEXIT_ENABLED |
> + KVM_X86_NOTIFY_VMEXIT_USER;
> + ret = kvm_vm_enable_cap(s, KVM_CAP_X86_NOTIFY_VMEXIT, 0,
> + notify_window_flags);
> + if (ret < 0) {
> + error_report("kvm: Failed to enable notify vmexit cap: %s",
> + strerror(-ret));
> + return ret;
> }
> }
>
> @@ -4940,6 +4952,7 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
> X86CPU *cpu = X86_CPU(cs);
> uint64_t code;
> int ret;
> + struct kvm_vcpu_events events = {};
>
> switch (run->exit_reason) {
> case KVM_EXIT_HLT:
> @@ -4995,6 +5008,19 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
> /* already handled in kvm_arch_post_run */
> ret = 0;
> break;
> + case KVM_EXIT_NOTIFY:
> + ret = 0;
> + if (run->notify.flags & KVM_NOTIFY_CONTEXT_INVALID) {
> + warn_report("KVM: invalid context due to notify vmexit");
> + if (has_triple_fault_event) {
> + events.flags |= KVM_VCPUEVENT_VALID_TRIPLE_FAULT;
> + events.triple_fault.pending = true;
> + ret = kvm_vcpu_ioctl(cs, KVM_SET_VCPU_EVENTS, &events);
> + } else {
> + ret = -1;
> + }
> + }
> + break;
> default:
> fprintf(stderr, "KVM: unknown exit reason %d\n", run->exit_reason);
> ret = -1;
> --
> 2.17.1
>
