[PATCH v3 1/2] KVM: VMX: Grab vmcs12 on CR8 interception update iff vCPU is in guest mode

[Sean Christopherson <seanjc@google.com>]

When updating CR8 intercepts, get vmcs12 if and only if the vCPU is in
guest mode so that a future change can have update CR8 intercepts during
vCPU creation, without running afoul of get_vmcs12()'s lockdep assertion.

  ------------[ cut here ]------------
  debug_locks && !(lock_is_held(&(&vcpu->mutex)->dep_map) || !refcount_read(&vcpu->kvm->users_count))
  WARNING: arch/x86/kvm/vmx/nested.h:61 at get_vmcs12 arch/x86/kvm/vmx/nested.h:60 [inline], CPU#0: syz.2.19/5879
  WARNING: arch/x86/kvm/vmx/nested.h:61 at vmx_update_cr8_intercept+0x3de/0x4e0 arch/x86/kvm/vmx/vmx.c:6879, CPU#0: syz.2.19/5879
  Modules linked in:
  CPU: 0 UID: 0 PID: 5879 Comm: syz.2.19 Not tainted syzkaller #0 PREEMPT(full)
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
  RIP: 0010:get_vmcs12 arch/x86/kvm/vmx/nested.h:60 [inline]
  RIP: 0010:vmx_update_cr8_intercept+0x3de/0x4e0 arch/x86/kvm/vmx/vmx.c:6879
  Call Trace:
   <TASK>
   apic_update_ppr arch/x86/kvm/lapic.c:984 [inline]
   kvm_lapic_reset+0x1c24/0x2980 arch/x86/kvm/lapic.c:3023
   kvm_vcpu_reset+0x44c/0x1bf0 arch/x86/kvm/x86.c:12986
   kvm_arch_vcpu_create+0x746/0x8b0 arch/x86/kvm/x86.c:12847
   kvm_vm_ioctl_create_vcpu+0x428/0x930 virt/kvm/kvm_main.c:4201
   kvm_vm_ioctl+0x893/0xd50 virt/kvm/kvm_main.c:5159
   vfs_ioctl fs/ioctl.c:51 [inline]
   __do_sys_ioctl fs/ioctl.c:597 [inline]
   __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
   do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   </TASK>

No functional change intended.

Reported-by: syzbot ci <syzbot+ci493c6d734b63e050@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/6a2adf3b.3b0a2d4e.8c8d1.0012.GAE@google.com
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a1a5edb39a7e..125994ed3db5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6872,11 +6872,10 @@ int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
 
 void vmx_update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
 {
-	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
 	int tpr_threshold;
 
 	if (is_guest_mode(vcpu) &&
-		nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW))
+	    nested_cpu_has(get_vmcs12(vcpu), CPU_BASED_TPR_SHADOW))
 		return;
 
 	guard(vmx_vmcs01)(vcpu);
-- 
2.55.0.rc0.738.g0c8ab3ebcc-goog