KVM: VMX: Do _all_ initialization before exposing /dev/kvm to userspace

[ Upstream commit 3c3b35a745e39e372db4e898299d4ef21051b6e3 ]

Call kvm_init() only after _all_ setup is complete, as kvm_init() exposes
/dev/kvm to userspace and thus allows userspace to create VMs (and call
other ioctls).  E.g. KVM will encounter a NULL pointer when attempting to
add a vCPU to the per-CPU loaded_vmcss_on_cpu list if userspace is able to
create a VM before vmx_init() configures said list.

 BUG: kernel NULL pointer dereference, address: 0000000000000008
 #PF: supervisor write access in kernel mode
 #PF: error_code(0x0002) - not-present page
 PGD 0 P4D 0
 Oops: 0002 [#1] SMP
 CPU: 6 PID: 1143 Comm: stable Not tainted 6.0.0-rc7+ #988
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
 RIP: 0010:vmx_vcpu_load_vmcs+0x68/0x230 [kvm_intel]
  <TASK>
  vmx_vcpu_load+0x16/0x60 [kvm_intel]
  kvm_arch_vcpu_load+0x32/0x1f0 [kvm]
  vcpu_load+0x2f/0x40 [kvm]
  kvm_arch_vcpu_create+0x231/0x310 [kvm]
  kvm_vm_ioctl+0x79f/0xe10 [kvm]
  ? handle_mm_fault+0xb1/0x220
  __x64_sys_ioctl+0x80/0xb0
  do_syscall_64+0x2b/0x50
  entry_SYSCALL_64_after_hwframe+0x46/0xb0
 RIP: 0033:0x7f5a6b05743b
  </TASK>
 Modules linked in: vhost_net vhost vhost_iotlb tap kvm_intel(+) kvm irqbypass

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221130230934.1014142-15-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 81a23ae4f872b84ad99ef2046550fe87842a2489..bc868958e91fe8c3b46767784cbb5dd3168b8367 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -8456,19 +8456,23 @@ static void vmx_cleanup_l1d_flush(void)
        l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
 }
 
-static void vmx_exit(void)
+static void __vmx_exit(void)
 {
+       allow_smaller_maxphyaddr = false;
+
 #ifdef CONFIG_KEXEC_CORE
        RCU_INIT_POINTER(crash_vmclear_loaded_vmcss, NULL);
        synchronize_rcu();
 #endif
+       vmx_cleanup_l1d_flush();
+}
 
+static void vmx_exit(void)
+{
        kvm_exit();
        kvm_x86_vendor_exit();
 
-       vmx_cleanup_l1d_flush();
-
-       allow_smaller_maxphyaddr = false;
+       __vmx_exit();
 }
 module_exit(vmx_exit);
 
@@ -8513,11 +8517,6 @@ static int __init vmx_init(void)
        if (r)
                return r;
 
-       r = kvm_init(&vmx_init_ops, sizeof(struct vcpu_vmx),
-                    __alignof__(struct vcpu_vmx), THIS_MODULE);
-       if (r)
-               goto err_kvm_init;
-
        /*
         * Must be called after common x86 init so enable_ept is properly set
         * up. Hand the parameter mitigation value in which was stored in
@@ -8551,11 +8550,20 @@ static int __init vmx_init(void)
        if (!enable_ept)
                allow_smaller_maxphyaddr = true;
 
+       /*
+        * Common KVM initialization _must_ come last, after this, /dev/kvm is
+        * exposed to userspace!
+        */
+       r = kvm_init(&vmx_init_ops, sizeof(struct vcpu_vmx),
+                    __alignof__(struct vcpu_vmx), THIS_MODULE);
+       if (r)
+               goto err_kvm_init;
+
        return 0;
 
-err_l1d_flush:
-       vmx_exit();
 err_kvm_init:
+       __vmx_exit();
+err_l1d_flush:
        kvm_x86_vendor_exit();
        return r;
 }