Subject: [PATCH] ARM: KVM: prevent NULL pointer dereference with KVM ioctl

From: [email-masked] (Christoffer Dall)
Date: Sun, 12 May 2013 22:13:52 -0700

On Wed, May 08, 2013 at 10:53:28AM +0100, Marc Zyngier wrote:
> On 07/05/13 13:55, Andre Przywara wrote:
> > Some ARM KVM VCPU ioctls require the vCPU to be properly initialized
> > with the KVM_ARM_VCPU_INIT ioctl before being used with further
> > requests. KVM_RUN checks whether this initialization has been
> > done, but other ioctls do not.
> > Namely KVM_GET_REG_LIST will dereference an array with index -1
> > without initialization and thus leads to a kernel oops.
> > Fix this by adding checks before executing the ioctl handlers.
> > 
> > Signed-off-by: Andre Przywara <[email-masked]>
> > ---
> >  arch/arm/kvm/arm.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> > index c1fe498..0c571ff 100644
> > --- a/arch/arm/kvm/arm.c
> > +++ b/arch/arm/kvm/arm.c
> > @@ -893,6 +893,11 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> >  	case KVM_SET_ONE_REG:
> >  	case KVM_GET_ONE_REG: {
> >  		struct kvm_one_reg reg;
> > +
> > +		/* Make sure they initialize the vcpu with KVM_ARM_VCPU_INIT */
> > +		if (unlikely(vcpu->arch.target < 0))
> > +			return -ENOEXEC;
> > +
> >  		if (copy_from_user(&reg, argp, sizeof(reg)))
> >  			return -EFAULT;
> >  		if (ioctl == KVM_SET_ONE_REG)
> > @@ -905,6 +910,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> >  		struct kvm_reg_list reg_list;
> >  		unsigned n;
> >  
> > +		/* Make sure they initialize the vcpu with KVM_ARM_VCPU_INIT */
> > +		if (unlikely(vcpu->arch.target < 0))
> > +			return -ENOEXEC;
> > +
> >  		if (copy_from_user(&reg_list, user_list, sizeof(reg_list)))
> >  			return -EFAULT;
> >  		n = reg_list.n;
> > 
> 
> So we also have the same snippet in kvm_arch_vcpu_ioctl_run().
> 
> Can you create a static function (kvm_vcpu_initialized?) containing that
> code and make all three sites use it?
> 
Andre, will you re-spin your patch as per Marc's comments?

Thanks,
-Christoffer