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

From: [email-masked] (Marc Zyngier)
Date: Wed, 08 May 2013 10:53:28 +0100

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?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...