Patch "KVM: VMX: Do _all_ initialization before exposing /dev/kvm to userspace" has been added to the 6.2-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 6.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-vmx-do-_all_-initialization-before-exposing-dev-.patch
and it can be found in the queue-6.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 6253ff63fe10e1ad8768d919baeac0e118cea4a6
Author: Sean Christopherson <seanjc@xxxxxxxxxx>
Date:   Wed Nov 30 23:08:58 2022 +0000

    KVM: VMX: Do _all_ initialization before exposing /dev/kvm to userspace
    
    [ Upstream commit e32b120071ea114efc0b4ddd439547750b85f618 ]
    
    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@xxxxxxxxxxxxxxx
    Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
    Message-Id: <20221130230934.1014142-15-seanjc@xxxxxxxxxx>
    Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 74be8b9030a3b..cb547a0833812 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -8521,19 +8521,23 @@ 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);
 
@@ -8578,11 +8582,6 @@ 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
@@ -8616,11 +8615,20 @@ 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;
 }