On 2/2/22 00:04, Tadeusz Struk wrote:

From: Sean Christopherson seanjc@google.com

Commit f7e570780efc5cec9b2ed1e0472a7da14e864fdb upstream.

Please apply it to 5.10.y. It fixes the following syzbot issue: Link: https://syzkaller.appspot.com/bug?id=c46ee6f22a68171154cdd9217216b2a02cf4b71...

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>

Cc: Sean Christopherson seanjc@google.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: stable@vger.kernel.org Cc: x86@kernel.org Cc: kvm@vger.kernel.org

Backported-by: Tadeusz Struk tadeusz.struk@linaro.org Signed-off-by: Sean Christopherson seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com

---

arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/svm/nested.c | 10 ++++++++-- arch/x86/kvm/svm/svm.c | 2 +- arch/x86/kvm/svm/svm.h | 2 +- arch/x86/kvm/vmx/nested.c | 1 + arch/x86/kvm/x86.c | 2 ++ 6 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index b1cd8334db11..078494401046 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1285,6 +1285,7 @@ struct kvm_x86_ops { }; struct kvm_x86_nested_ops {

• void (*leave_nested)(struct kvm_vcpu *vcpu); int (*check_events)(struct kvm_vcpu *vcpu); bool (*hv_timer_pending)(struct kvm_vcpu *vcpu); int (*get_state)(struct kvm_vcpu *vcpu,

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index f0946872f5e6..23910e6a3f01 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -783,8 +783,10 @@ void svm_free_nested(struct vcpu_svm *svm) /*

• Forcibly leave nested mode in order to be able to reset the VCPU later on.

*/ -void svm_leave_nested(struct vcpu_svm *svm) +void svm_leave_nested(struct kvm_vcpu *vcpu) {

• struct vcpu_svm *svm = to_svm(vcpu);
• if (is_guest_mode(&svm->vcpu)) { struct vmcb *hsave = svm->nested.hsave; struct vmcb *vmcb = svm->vmcb;

@@ -1185,7 +1187,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, return -EINVAL; if (!(kvm_state->flags & KVM_STATE_NESTED_GUEST_MODE)) {

• svm_leave_nested(svm);
  

• svm_leave_nested(vcpu);
  

  svm_set_gif(svm, !!(kvm_state->flags & KVM_STATE_NESTED_GIF_SET)); return 0; }

@@ -1238,6 +1240,9 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, copy_vmcb_control_area(&hsave->control, &svm->vmcb->control); hsave->save = *save;

• if (is_guest_mode(vcpu))

• svm_leave_nested(vcpu);
  

• svm->nested.vmcb12_gpa = kvm_state->hdr.svm.vmcb_pa; load_nested_vmcb_control(svm, ctl); nested_prepare_vmcb_control(svm);

@@ -1252,6 +1257,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, } struct kvm_x86_nested_ops svm_nested_ops = {

• .leave_nested = svm_leave_nested, .check_events = svm_check_nested_events, .get_nested_state_pages = svm_get_nested_state_pages, .get_state = svm_get_nested_state,

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 5e1d7396a6b8..b4f4ce5ace6b 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -279,7 +279,7 @@ int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer) if ((old_efer & EFER_SVME) != (efer & EFER_SVME)) { if (!(efer & EFER_SVME)) {

• 	svm_leave_nested(svm);
  

• 	svm_leave_nested(vcpu);
  svm_set_gif(svm, true);
  

/* diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index be74e22b82ea..2c007241fbf5 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -393,7 +393,7 @@ static inline bool nested_exit_on_nmi(struct vcpu_svm *svm) int enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa, struct vmcb *nested_vmcb); -void svm_leave_nested(struct vcpu_svm *svm); +void svm_leave_nested(struct kvm_vcpu *vcpu); void svm_free_nested(struct vcpu_svm *svm); int svm_allocate_nested(struct vcpu_svm *svm); int nested_svm_vmrun(struct vcpu_svm *svm); diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index d5f24a2f3e91..6a4b91b77cde 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -6614,6 +6614,7 @@ __init int nested_vmx_hardware_setup(int (*exit_handlers[])(struct kvm_vcpu *)) } struct kvm_x86_nested_ops vmx_nested_ops = {

• .leave_nested = vmx_leave_nested, .check_events = vmx_check_nested_events, .hv_timer_pending = nested_vmx_preemption_timer_pending, .get_state = vmx_get_nested_state,

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b885063dc393..ab31745c04d0 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4390,6 +4390,8 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu, vcpu->arch.hflags |= HF_SMM_MASK; else vcpu->arch.hflags &= ~HF_SMM_MASK;

• 	kvm_x86_ops.nested_ops->leave_nested(vcpu);
  kvm_smm_changed(vcpu);
  

  }

Acked-by: Paolo Bonzini pbonzini@redhat.com

Paolo