| Message ID | 20220915092839.5518-3-chenyi.qiang@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Enable notify VM exit | expand |
On Thu, Sep 15, 2022 at 05:28:39PM +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 ... > > Note that notify_window is only valid when notify_vmexit is on. The valid > range of notify_window is non-negative. It is even safe to set it to zero > since there's an internal hardware threshold to be added to ensure no false > positive. > > 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@intel.com> > --- > hw/i386/x86.c | 45 +++++++++++++++++++++++++++++++++++++++++++ > include/hw/i386/x86.h | 5 +++++ > qemu-options.hx | 10 +++++++++- > target/i386/kvm/kvm.c | 28 +++++++++++++++++++++++++++ > 4 files changed, 87 insertions(+), 1 deletion(-) > > diff --git a/hw/i386/x86.c b/hw/i386/x86.c > index 050eedc0c8..1eccbd3deb 100644 > --- a/hw/i386/x86.c > +++ b/hw/i386/x86.c > @@ -1379,6 +1379,37 @@ 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); > @@ -1392,6 +1423,8 @@ static void x86_machine_initfn(Object *obj) > x86ms->oem_table_id = g_strndup(ACPI_BUILD_APPNAME8, 8); > x86ms->bus_lock_ratelimit = 0; > x86ms->above_4g_mem_start = 4 * GiB; > + x86ms->notify_vmexit = false; > + x86ms->notify_window = 0; > } > > static void x86_machine_class_init(ObjectClass *oc, void *data) > @@ -1461,6 +1494,18 @@ 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 62fa5774f8..5707329fa7 100644 > --- a/include/hw/i386/x86.h > +++ b/include/hw/i386/x86.h > @@ -85,6 +85,9 @@ 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" > @@ -94,6 +97,8 @@ 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/qemu-options.hx b/qemu-options.hx > index 31c04f7eea..3cdeeac8f3 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -37,7 +37,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \ > " memory-encryption=@var{} memory encryption object to use (default=none)\n" > " hmat=on|off controls ACPI HMAT support (default=off)\n" > " memory-backend='backend-id' specifies explicitly provided backend for main RAM (default=none)\n" > - " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n", > + " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n" > + " notify_vmexit=on|off,notify_window=n controls notify VM exit support (default=off) and specifies the notify window size (default=0)\n", > QEMU_ARCH_ALL) > SRST > ``-machine [type=]name[,prop=value[,...]]`` > @@ -157,6 +158,13 @@ SRST > :: > > -machine cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.targets.1=cxl.1,cxl-fmw.0.size=128G,cxl-fmw.0.interleave-granularity=512k > + > + ``notify_vmexit=on|off,notify_window=n`` > + Enables or disables Notify VM exit support on x86 host and specify > + the corresponding notify window to trigger the VM exit if enabled. > + This feature can mitigate the CPU stuck issue due to event windows > + don't open up for a specified of time (notify window). > + The default is off. > ERST > > DEF("M", HAS_ARG, QEMU_OPTION_M, > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > index 3838827134..ae7fb2c495 100644 > --- a/target/i386/kvm/kvm.c > +++ b/target/i386/kvm/kvm.c > @@ -2597,6 +2597,20 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > 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; It'll always request a user exit here as long as enabled, then... > + 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; > + } > + } > } > > return 0; > @@ -5141,6 +5155,7 @@ 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: > @@ -5196,6 +5211,19 @@ 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; > + } > + } ... should we do something even if the context is valid? Or I'm a bit confused why KVM_X86_NOTIFY_VMEXIT_USER was set (IIUC we can just enable it without setting VMEXIT_USER then). Not sure some warning would be also useful here, but I really don't know the whole context so I can't tell whether there can easily be false positives to pollute qemu log. > + break; > default: > fprintf(stderr, "KVM: unknown exit reason %d\n", run->exit_reason); > ret = -1; > -- > 2.17.1 >
On 9/17/2022 5:57 AM, Peter Xu wrote: > On Thu, Sep 15, 2022 at 05:28:39PM +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 ... >> >> Note that notify_window is only valid when notify_vmexit is on. The valid >> range of notify_window is non-negative. It is even safe to set it to zero >> since there's an internal hardware threshold to be added to ensure no false >> positive. >> >> 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@intel.com> >> --- >> hw/i386/x86.c | 45 +++++++++++++++++++++++++++++++++++++++++++ >> include/hw/i386/x86.h | 5 +++++ >> qemu-options.hx | 10 +++++++++- >> target/i386/kvm/kvm.c | 28 +++++++++++++++++++++++++++ >> 4 files changed, 87 insertions(+), 1 deletion(-) >> >> diff --git a/hw/i386/x86.c b/hw/i386/x86.c >> index 050eedc0c8..1eccbd3deb 100644 >> --- a/hw/i386/x86.c >> +++ b/hw/i386/x86.c >> @@ -1379,6 +1379,37 @@ 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); >> @@ -1392,6 +1423,8 @@ static void x86_machine_initfn(Object *obj) >> x86ms->oem_table_id = g_strndup(ACPI_BUILD_APPNAME8, 8); >> x86ms->bus_lock_ratelimit = 0; >> x86ms->above_4g_mem_start = 4 * GiB; >> + x86ms->notify_vmexit = false; >> + x86ms->notify_window = 0; >> } >> >> static void x86_machine_class_init(ObjectClass *oc, void *data) >> @@ -1461,6 +1494,18 @@ 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 62fa5774f8..5707329fa7 100644 >> --- a/include/hw/i386/x86.h >> +++ b/include/hw/i386/x86.h >> @@ -85,6 +85,9 @@ 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" >> @@ -94,6 +97,8 @@ 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/qemu-options.hx b/qemu-options.hx >> index 31c04f7eea..3cdeeac8f3 100644 >> --- a/qemu-options.hx >> +++ b/qemu-options.hx >> @@ -37,7 +37,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \ >> " memory-encryption=@var{} memory encryption object to use (default=none)\n" >> " hmat=on|off controls ACPI HMAT support (default=off)\n" >> " memory-backend='backend-id' specifies explicitly provided backend for main RAM (default=none)\n" >> - " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n", >> + " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n" >> + " notify_vmexit=on|off,notify_window=n controls notify VM exit support (default=off) and specifies the notify window size (default=0)\n", >> QEMU_ARCH_ALL) >> SRST >> ``-machine [type=]name[,prop=value[,...]]`` >> @@ -157,6 +158,13 @@ SRST >> :: >> >> -machine cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.targets.1=cxl.1,cxl-fmw.0.size=128G,cxl-fmw.0.interleave-granularity=512k >> + >> + ``notify_vmexit=on|off,notify_window=n`` >> + Enables or disables Notify VM exit support on x86 host and specify >> + the corresponding notify window to trigger the VM exit if enabled. >> + This feature can mitigate the CPU stuck issue due to event windows >> + don't open up for a specified of time (notify window). >> + The default is off. >> ERST >> >> DEF("M", HAS_ARG, QEMU_OPTION_M, >> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c >> index 3838827134..ae7fb2c495 100644 >> --- a/target/i386/kvm/kvm.c >> +++ b/target/i386/kvm/kvm.c >> @@ -2597,6 +2597,20 @@ int kvm_arch_init(MachineState *ms, KVMState *s) >> 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; > > It'll always request a user exit here as long as enabled, then... > >> + 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; >> + } >> + } >> } >> >> return 0; >> @@ -5141,6 +5155,7 @@ 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: >> @@ -5196,6 +5211,19 @@ 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; >> + } >> + } > > ... should we do something even if the context is valid? Or I'm a bit Yes, make sense. A warning log is necessary if the context is valid. > confused why KVM_X86_NOTIFY_VMEXIT_USER was set (IIUC we can just enable it > without setting VMEXIT_USER then). > VMEXIT_USR was set because KVM community prefers userspace can get notified and help to do some analysis or mitigation if notify window was exceeded. > Not sure some warning would be also useful here, but I really don't know > the whole context so I can't tell whether there can easily be false > positives to pollute qemu log. > The false positive case is not easy to happen unless some potential issues in silicon. But in case of it, to avoid polluting qemu log, how about: diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index ae7fb2c495..8f97133cbf 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -5213,6 +5213,7 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run) break; case KVM_EXIT_NOTIFY: ret = 0; + warn_report_once("KVM: notify window was exceeded in guest"); if (run->notify.flags & KVM_NOTIFY_CONTEXT_INVALID) { warn_report("KVM: invalid context due to notify vmexit"); if (has_triple_fault_event) { >> + break; >> default: >> fprintf(stderr, "KVM: unknown exit reason %d\n", run->exit_reason); >> ret = -1; >> -- >> 2.17.1 >> >
On 9/19/2022 1:46 PM, Chenyi Qiang wrote: >> Not sure some warning would be also useful here, but I really don't know >> the whole context so I can't tell whether there can easily be false >> positives to pollute qemu log. >> > > The false positive case is not easy to happen unless some potential > issues in silicon. But in case of it, to avoid polluting qemu log, how > about: > > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > index ae7fb2c495..8f97133cbf 100644 > --- a/target/i386/kvm/kvm.c > +++ b/target/i386/kvm/kvm.c > @@ -5213,6 +5213,7 @@ int kvm_arch_handle_exit(CPUState *cs, struct > kvm_run *run) > break; > case KVM_EXIT_NOTIFY: > ret = 0; > + warn_report_once("KVM: notify window was exceeded in guest"); > if (run->notify.flags & KVM_NOTIFY_CONTEXT_INVALID) { > warn_report("KVM: invalid context due to notify vmexit"); > if (has_triple_fault_event) { how about this case KVM_EXIT_NOTIFY: bool ctx_invalid = run->notify.flags & KVM_NOTIFY_CONTEXT_INVALID; ret = 0; warn_report_once("KVM: Encounter notify exit with %svalid context", ctx_invalid ? "in" : ""); if (ctx_invalid) { ... }
On Mon, Sep 19, 2022 at 01:46:38PM +0800, Chenyi Qiang wrote: > > > On 9/17/2022 5:57 AM, Peter Xu wrote: > > On Thu, Sep 15, 2022 at 05:28:39PM +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 ... > > > > > > Note that notify_window is only valid when notify_vmexit is on. The valid > > > range of notify_window is non-negative. It is even safe to set it to zero > > > since there's an internal hardware threshold to be added to ensure no false > > > positive. > > > > > > 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@intel.com> > > > --- > > > hw/i386/x86.c | 45 +++++++++++++++++++++++++++++++++++++++++++ > > > include/hw/i386/x86.h | 5 +++++ > > > qemu-options.hx | 10 +++++++++- > > > target/i386/kvm/kvm.c | 28 +++++++++++++++++++++++++++ > > > 4 files changed, 87 insertions(+), 1 deletion(-) > > > > > > diff --git a/hw/i386/x86.c b/hw/i386/x86.c > > > index 050eedc0c8..1eccbd3deb 100644 > > > --- a/hw/i386/x86.c > > > +++ b/hw/i386/x86.c > > > @@ -1379,6 +1379,37 @@ 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); > > > @@ -1392,6 +1423,8 @@ static void x86_machine_initfn(Object *obj) > > > x86ms->oem_table_id = g_strndup(ACPI_BUILD_APPNAME8, 8); > > > x86ms->bus_lock_ratelimit = 0; > > > x86ms->above_4g_mem_start = 4 * GiB; > > > + x86ms->notify_vmexit = false; > > > + x86ms->notify_window = 0; > > > } > > > static void x86_machine_class_init(ObjectClass *oc, void *data) > > > @@ -1461,6 +1494,18 @@ 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 62fa5774f8..5707329fa7 100644 > > > --- a/include/hw/i386/x86.h > > > +++ b/include/hw/i386/x86.h > > > @@ -85,6 +85,9 @@ 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" > > > @@ -94,6 +97,8 @@ 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/qemu-options.hx b/qemu-options.hx > > > index 31c04f7eea..3cdeeac8f3 100644 > > > --- a/qemu-options.hx > > > +++ b/qemu-options.hx > > > @@ -37,7 +37,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \ > > > " memory-encryption=@var{} memory encryption object to use (default=none)\n" > > > " hmat=on|off controls ACPI HMAT support (default=off)\n" > > > " memory-backend='backend-id' specifies explicitly provided backend for main RAM (default=none)\n" > > > - " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n", > > > + " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n" > > > + " notify_vmexit=on|off,notify_window=n controls notify VM exit support (default=off) and specifies the notify window size (default=0)\n", > > > QEMU_ARCH_ALL) > > > SRST > > > ``-machine [type=]name[,prop=value[,...]]`` > > > @@ -157,6 +158,13 @@ SRST > > > :: > > > -machine cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.targets.1=cxl.1,cxl-fmw.0.size=128G,cxl-fmw.0.interleave-granularity=512k > > > + > > > + ``notify_vmexit=on|off,notify_window=n`` > > > + Enables or disables Notify VM exit support on x86 host and specify > > > + the corresponding notify window to trigger the VM exit if enabled. > > > + This feature can mitigate the CPU stuck issue due to event windows > > > + don't open up for a specified of time (notify window). > > > + The default is off. > > > ERST > > > DEF("M", HAS_ARG, QEMU_OPTION_M, > > > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > > > index 3838827134..ae7fb2c495 100644 > > > --- a/target/i386/kvm/kvm.c > > > +++ b/target/i386/kvm/kvm.c > > > @@ -2597,6 +2597,20 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > > > 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; > > > > It'll always request a user exit here as long as enabled, then... > > > > > + 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; > > > + } > > > + } > > > } > > > return 0; > > > @@ -5141,6 +5155,7 @@ 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: > > > @@ -5196,6 +5211,19 @@ 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; > > > + } > > > + } > > > > ... should we do something even if the context is valid? Or I'm a bit > > > Yes, make sense. A warning log is necessary if the context is valid. > > > confused why KVM_X86_NOTIFY_VMEXIT_USER was set (IIUC we can just enable it > > without setting VMEXIT_USER then). > > > > VMEXIT_USR was set because KVM community prefers userspace can get notified > and help to do some analysis or mitigation if notify window was exceeded. > > > Not sure some warning would be also useful here, but I really don't know > > the whole context so I can't tell whether there can easily be false > > positives to pollute qemu log. > > > > The false positive case is not easy to happen unless some potential issues > in silicon. But in case of it, to avoid polluting qemu log, how about: > > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > index ae7fb2c495..8f97133cbf 100644 > --- a/target/i386/kvm/kvm.c > +++ b/target/i386/kvm/kvm.c > @@ -5213,6 +5213,7 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run > *run) > break; > case KVM_EXIT_NOTIFY: > ret = 0; > + warn_report_once("KVM: notify window was exceeded in guest"); Is there more informative way to dump this? If it's 99% that the guest was doing something weird and needs attention, maybe worthwhile to point that out directly to the admin? > if (run->notify.flags & KVM_NOTIFY_CONTEXT_INVALID) { > warn_report("KVM: invalid context due to notify vmexit"); > if (has_triple_fault_event) { Adding a warning looks good to me, with that (or in any better form of wording): Acked-by: Peter Xu <peterx@redhat.com> Thanks,
On 9/19/2022 11:53 PM, Peter Xu wrote: > On Mon, Sep 19, 2022 at 01:46:38PM +0800, Chenyi Qiang wrote: >> >> >> On 9/17/2022 5:57 AM, Peter Xu wrote: >>> On Thu, Sep 15, 2022 at 05:28:39PM +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 ... >>>> >>>> Note that notify_window is only valid when notify_vmexit is on. The valid >>>> range of notify_window is non-negative. It is even safe to set it to zero >>>> since there's an internal hardware threshold to be added to ensure no false >>>> positive. >>>> >>>> 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@intel.com> >>>> --- >>>> hw/i386/x86.c | 45 +++++++++++++++++++++++++++++++++++++++++++ >>>> include/hw/i386/x86.h | 5 +++++ >>>> qemu-options.hx | 10 +++++++++- >>>> target/i386/kvm/kvm.c | 28 +++++++++++++++++++++++++++ >>>> 4 files changed, 87 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/hw/i386/x86.c b/hw/i386/x86.c >>>> index 050eedc0c8..1eccbd3deb 100644 >>>> --- a/hw/i386/x86.c >>>> +++ b/hw/i386/x86.c >>>> @@ -1379,6 +1379,37 @@ 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); >>>> @@ -1392,6 +1423,8 @@ static void x86_machine_initfn(Object *obj) >>>> x86ms->oem_table_id = g_strndup(ACPI_BUILD_APPNAME8, 8); >>>> x86ms->bus_lock_ratelimit = 0; >>>> x86ms->above_4g_mem_start = 4 * GiB; >>>> + x86ms->notify_vmexit = false; >>>> + x86ms->notify_window = 0; >>>> } >>>> static void x86_machine_class_init(ObjectClass *oc, void *data) >>>> @@ -1461,6 +1494,18 @@ 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 62fa5774f8..5707329fa7 100644 >>>> --- a/include/hw/i386/x86.h >>>> +++ b/include/hw/i386/x86.h >>>> @@ -85,6 +85,9 @@ 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" >>>> @@ -94,6 +97,8 @@ 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/qemu-options.hx b/qemu-options.hx >>>> index 31c04f7eea..3cdeeac8f3 100644 >>>> --- a/qemu-options.hx >>>> +++ b/qemu-options.hx >>>> @@ -37,7 +37,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \ >>>> " memory-encryption=@var{} memory encryption object to use (default=none)\n" >>>> " hmat=on|off controls ACPI HMAT support (default=off)\n" >>>> " memory-backend='backend-id' specifies explicitly provided backend for main RAM (default=none)\n" >>>> - " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n", >>>> + " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n" >>>> + " notify_vmexit=on|off,notify_window=n controls notify VM exit support (default=off) and specifies the notify window size (default=0)\n", >>>> QEMU_ARCH_ALL) >>>> SRST >>>> ``-machine [type=]name[,prop=value[,...]]`` >>>> @@ -157,6 +158,13 @@ SRST >>>> :: >>>> -machine cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.targets.1=cxl.1,cxl-fmw.0.size=128G,cxl-fmw.0.interleave-granularity=512k >>>> + >>>> + ``notify_vmexit=on|off,notify_window=n`` >>>> + Enables or disables Notify VM exit support on x86 host and specify >>>> + the corresponding notify window to trigger the VM exit if enabled. >>>> + This feature can mitigate the CPU stuck issue due to event windows >>>> + don't open up for a specified of time (notify window). >>>> + The default is off. >>>> ERST >>>> DEF("M", HAS_ARG, QEMU_OPTION_M, >>>> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c >>>> index 3838827134..ae7fb2c495 100644 >>>> --- a/target/i386/kvm/kvm.c >>>> +++ b/target/i386/kvm/kvm.c >>>> @@ -2597,6 +2597,20 @@ int kvm_arch_init(MachineState *ms, KVMState *s) >>>> 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; >>> >>> It'll always request a user exit here as long as enabled, then... >>> >>>> + 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; >>>> + } >>>> + } >>>> } >>>> return 0; >>>> @@ -5141,6 +5155,7 @@ 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: >>>> @@ -5196,6 +5211,19 @@ 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; >>>> + } >>>> + } >>> >>> ... should we do something even if the context is valid? Or I'm a bit >> >> >> Yes, make sense. A warning log is necessary if the context is valid. >> >>> confused why KVM_X86_NOTIFY_VMEXIT_USER was set (IIUC we can just enable it >>> without setting VMEXIT_USER then). >>> >> >> VMEXIT_USR was set because KVM community prefers userspace can get notified >> and help to do some analysis or mitigation if notify window was exceeded. >> >>> Not sure some warning would be also useful here, but I really don't know >>> the whole context so I can't tell whether there can easily be false >>> positives to pollute qemu log. >>> >> >> The false positive case is not easy to happen unless some potential issues >> in silicon. But in case of it, to avoid polluting qemu log, how about: >> >> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c >> index ae7fb2c495..8f97133cbf 100644 >> --- a/target/i386/kvm/kvm.c >> +++ b/target/i386/kvm/kvm.c >> @@ -5213,6 +5213,7 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run >> *run) >> break; >> case KVM_EXIT_NOTIFY: >> ret = 0; >> + warn_report_once("KVM: notify window was exceeded in guest"); > > Is there more informative way to dump this? If it's 99% that the guest was > doing something weird and needs attention, maybe worthwhile to point that > out directly to the admin? > Do you mean to use other method to dump the info? i.e. printing a message is not so clear. Or the output message ("KVM: notify window was exceeded in guest") is not obvious and we need other wording. >> if (run->notify.flags & KVM_NOTIFY_CONTEXT_INVALID) { >> warn_report("KVM: invalid context due to notify vmexit"); >> if (has_triple_fault_event) { > > Adding a warning looks good to me, with that (or in any better form of > wording): > If no objection, I'll follow Xiaoyao's suggestion to form the wording like: case KVM_EXIT_NOTIFY: ctx_invalid = !!(run->notify.flags & KVM_NOTIFY_CONTEXT_INVALID); ret = 0; warn_report_once("KVM: Encounter notify exit with %svalid context in guest", ctx_invalid ? "in" : ""); if (ctx_invalid) { if (has_triple_fault_event) {} } > Acked-by: Peter Xu <peterx@redhat.com> > > Thanks, >
On Tue, Sep 20, 2022 at 01:55:20PM +0800, Chenyi Qiang wrote: > > > @@ -5213,6 +5213,7 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run > > > *run) > > > break; > > > case KVM_EXIT_NOTIFY: > > > ret = 0; > > > + warn_report_once("KVM: notify window was exceeded in guest"); > > > > Is there more informative way to dump this? If it's 99% that the guest was > > doing something weird and needs attention, maybe worthwhile to point that > > out directly to the admin? > > > > Do you mean to use other method to dump the info? i.e. printing a message is > not so clear. Or the output message ("KVM: notify window was exceeded in > guest") is not obvious and we need other wording. I meant something like: KVM received notify exit. It means there can be possible misbehaves in the guest, please have a look. Or something similar. What I'm worried is the admin may not understand what's "notify window" and that message got simply ignored. Though I am not even sure whether that's accurate in the wordings. > > > > if (run->notify.flags & KVM_NOTIFY_CONTEXT_INVALID) { > > > warn_report("KVM: invalid context due to notify vmexit"); > > > if (has_triple_fault_event) { > > > > Adding a warning looks good to me, with that (or in any better form of > > wording): > > > If no objection, I'll follow Xiaoyao's suggestion to form the wording like: No objection here. Thanks.
On 9/20/2022 9:59 PM, Peter Xu wrote: > On Tue, Sep 20, 2022 at 01:55:20PM +0800, Chenyi Qiang wrote: >>>> @@ -5213,6 +5213,7 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run >>>> *run) >>>> break; >>>> case KVM_EXIT_NOTIFY: >>>> ret = 0; >>>> + warn_report_once("KVM: notify window was exceeded in guest"); >>> >>> Is there more informative way to dump this? If it's 99% that the guest was >>> doing something weird and needs attention, maybe worthwhile to point that >>> out directly to the admin? >>> >> >> Do you mean to use other method to dump the info? i.e. printing a message is >> not so clear. Or the output message ("KVM: notify window was exceeded in >> guest") is not obvious and we need other wording. > > I meant something like: > > KVM received notify exit. It means there can be possible misbehaves in > the guest, please have a look. Get your point. Then I can print this message behind as well. Thanks. > > Or something similar. What I'm worried is the admin may not understand > what's "notify window" and that message got simply ignored. > > Though I am not even sure whether that's accurate in the wordings. > >> >>>> if (run->notify.flags & KVM_NOTIFY_CONTEXT_INVALID) { >>>> warn_report("KVM: invalid context due to notify vmexit"); >>>> if (has_triple_fault_event) { >>> >>> Adding a warning looks good to me, with that (or in any better form of >>> wording): >>> >> If no objection, I'll follow Xiaoyao's suggestion to form the wording like: > > No objection here. Thanks. >
diff --git a/hw/i386/x86.c b/hw/i386/x86.c index 050eedc0c8..1eccbd3deb 100644 --- a/hw/i386/x86.c +++ b/hw/i386/x86.c @@ -1379,6 +1379,37 @@ 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); @@ -1392,6 +1423,8 @@ static void x86_machine_initfn(Object *obj) x86ms->oem_table_id = g_strndup(ACPI_BUILD_APPNAME8, 8); x86ms->bus_lock_ratelimit = 0; x86ms->above_4g_mem_start = 4 * GiB; + x86ms->notify_vmexit = false; + x86ms->notify_window = 0; } static void x86_machine_class_init(ObjectClass *oc, void *data) @@ -1461,6 +1494,18 @@ 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 62fa5774f8..5707329fa7 100644 --- a/include/hw/i386/x86.h +++ b/include/hw/i386/x86.h @@ -85,6 +85,9 @@ 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" @@ -94,6 +97,8 @@ 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/qemu-options.hx b/qemu-options.hx index 31c04f7eea..3cdeeac8f3 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -37,7 +37,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \ " memory-encryption=@var{} memory encryption object to use (default=none)\n" " hmat=on|off controls ACPI HMAT support (default=off)\n" " memory-backend='backend-id' specifies explicitly provided backend for main RAM (default=none)\n" - " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n", + " cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n" + " notify_vmexit=on|off,notify_window=n controls notify VM exit support (default=off) and specifies the notify window size (default=0)\n", QEMU_ARCH_ALL) SRST ``-machine [type=]name[,prop=value[,...]]`` @@ -157,6 +158,13 @@ SRST :: -machine cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.targets.1=cxl.1,cxl-fmw.0.size=128G,cxl-fmw.0.interleave-granularity=512k + + ``notify_vmexit=on|off,notify_window=n`` + Enables or disables Notify VM exit support on x86 host and specify + the corresponding notify window to trigger the VM exit if enabled. + This feature can mitigate the CPU stuck issue due to event windows + don't open up for a specified of time (notify window). + The default is off. ERST DEF("M", HAS_ARG, QEMU_OPTION_M, diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index 3838827134..ae7fb2c495 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -2597,6 +2597,20 @@ int kvm_arch_init(MachineState *ms, KVMState *s) 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; + } + } } return 0; @@ -5141,6 +5155,7 @@ 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: @@ -5196,6 +5211,19 @@ 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;
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 ... Note that notify_window is only valid when notify_vmexit is on. The valid range of notify_window is non-negative. It is even safe to set it to zero since there's an internal hardware threshold to be added to ensure no false positive. 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@intel.com> --- hw/i386/x86.c | 45 +++++++++++++++++++++++++++++++++++++++++++ include/hw/i386/x86.h | 5 +++++ qemu-options.hx | 10 +++++++++- target/i386/kvm/kvm.c | 28 +++++++++++++++++++++++++++ 4 files changed, 87 insertions(+), 1 deletion(-)