KVM: x86: Forcibly leave nested virt when SMM state is toggled

In the Linux kernel, the following vulnerability has been resolved:

KVM: x86: Forcibly leave nested virt when SMM state is toggled

Forcibly leave nested virtualization operation if userspace toggles SMM

state via KVM_SET_VCPU_EVENTS or KVM_SYNC_X86_EVENTS. If userspace

forces the vCPU out of SMM while it's post-VMXON and then injects an SMI,

vmx_enter_smm() will overwrite vmx->nested.smm.vmxon and end up with both

vmxon=false and smm.vmxon=false, but all other nVMX state allocated.

Don't attempt to gracefully handle the transition as (a) most transitions

are nonsencial, e.g. forcing SMM while L2 is running, (b) there isn't

sufficient information to handle all transitions, e.g. SVM wants access

to the SMRAM save state, and (c) KVM_SET_VCPU_EVENTS must precede

KVM_SET_NESTED_STATE during state restore as the latter disallows putting

the vCPU into L2 if SMM is active, and disallows tagging the vCPU as

being post-VMXON in SMM if SMM is not active.

Abuse of KVM_SET_VCPU_EVENTS manifests as a WARN and memory leak in nVMX

due to failure to free vmcs01's shadow VMCS, but the bug goes far beyond

just a memory leak, e.g. toggling SMM on while L2 is active puts the vCPU

in an architecturally impossible state.

WARNING: CPU: 0 PID: 3606 at free_loaded_vmcs arch/x86/kvm/vmx/vmx.c:2665 [inline]

WARNING: CPU: 0 PID: 3606 at free_loaded_vmcs+0x158/0x1a0 arch/x86/kvm/vmx/vmx.c:2656

Modules linked in:

CPU: 1 PID: 3606 Comm: syz-executor725 Not tainted 5.17.0-rc1-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

RIP: 0010:free_loaded_vmcs arch/x86/kvm/vmx/vmx.c:2665 [inline]

RIP: 0010:free_loaded_vmcs+0x158/0x1a0 arch/x86/kvm/vmx/vmx.c:2656

Code: <0f> 0b eb b3 e8 8f 4d 9f 00 e9 f7 fe ff ff 48 89 df e8 92 4d 9f 00

Call Trace:

<TASK>

kvm_arch_vcpu_destroy+0x72/0x2f0 arch/x86/kvm/x86.c:11123

kvm_vcpu_destroy arch/x86/kvm/../../../virt/kvm/kvm_main.c:441 [inline]

kvm_destroy_vcpus+0x11f/0x290 arch/x86/kvm/../../../virt/kvm/kvm_main.c:460

kvm_free_vcpus arch/x86/kvm/x86.c:11564 [inline]

kvm_arch_destroy_vm+0x2e8/0x470 arch/x86/kvm/x86.c:11676

kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:1217 [inline]

kvm_put_kvm+0x4fa/0xb00 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1250

kvm_vm_release+0x3f/0x50 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1273

__fput+0x286/0x9f0 fs/file_table.c:311

task_work_run+0xdd/0x1a0 kernel/task_work.c:164

exit_task_work include/linux/task_work.h:32 [inline]

do_exit+0xb29/0x2a30 kernel/exit.c:806

do_group_exit+0xd2/0x2f0 kernel/exit.c:935

get_signal+0x4b0/0x28c0 kernel/signal.c:2862

arch_do_signal_or_restart+0x2a9/0x1c40 arch/x86/kernel/signal.c:868

handle_signal_work kernel/entry/common.c:148 [inline]

exit_to_user_mode_loop kernel/entry/common.c:172 [inline]

exit_to_user_mode_prepare+0x17d/0x290 kernel/entry/common.c:207

__syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]

syscall_exit_to_user_mode+0x19/0x60 kernel/entry/common.c:300

do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86

entry_SYSCALL_64_after_hwframe+0x44/0xae

</TASK>