linux-kernel - Re: [PATCH v2] KVM: s390: Do not leak kernel stack data in the KVM_S390

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Date:   Thu, 12 Sep 2019 14:14:29 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Thomas Huth <thuth@...hat.com>,
        Janosch Frank <frankja@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] KVM: s390: Do not leak kernel stack data in the
 KVM_S390_INTERRUPT ioctl

thanks, applied and queued for 5.3 (need to do some regression testing before
sending out)

On 12.09.19 13:54, Thomas Huth wrote:
> When the userspace program runs the KVM_S390_INTERRUPT ioctl to inject
> an interrupt, we convert them from the legacy struct kvm_s390_interrupt
> to the new struct kvm_s390_irq via the s390int_to_s390irq() function.
> However, this function does not take care of all types of interrupts
> that we can inject into the guest later (see do_inject_vcpu()). Since we
> do not clear out the s390irq values before calling s390int_to_s390irq(),
> there is a chance that we copy random data from the kernel stack which
> could be leaked to the userspace later.
> 
> Specifically, the problem exists with the KVM_S390_INT_PFAULT_INIT
> interrupt: s390int_to_s390irq() does not handle it, and the function
> __inject_pfault_init() later copies irq->u.ext which contains the
> random kernel stack data. This data can then be leaked either to
> the guest memory in __deliver_pfault_init(), or the userspace might
> retrieve it directly with the KVM_S390_GET_IRQ_STATE ioctl.
> 
> Fix it by handling that interrupt type in s390int_to_s390irq(), too,
> and by making sure that the s390irq struct is properly pre-initialized.
> And while we're at it, make sure that s390int_to_s390irq() now
> directly returns -EINVAL for unknown interrupt types, so that we
> immediately get a proper error code in case we add more interrupt
> types to do_inject_vcpu() without updating s390int_to_s390irq()
> sometime in the future.
> 
> Cc: stable@...r.kernel.org
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>
> Signed-off-by: Thomas Huth <thuth@...hat.com>
> ---
>  arch/s390/kvm/interrupt.c | 10 ++++++++++
>  arch/s390/kvm/kvm-s390.c  |  2 +-
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index 3e7efdd9228a..165dea4c7f19 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -1960,6 +1960,16 @@ int s390int_to_s390irq(struct kvm_s390_interrupt *s390int,
>  	case KVM_S390_MCHK:
>  		irq->u.mchk.mcic = s390int->parm64;
>  		break;
> +	case KVM_S390_INT_PFAULT_INIT:
> +		irq->u.ext.ext_params = s390int->parm;
> +		irq->u.ext.ext_params2 = s390int->parm64;
> +		break;
> +	case KVM_S390_RESTART:
> +	case KVM_S390_INT_CLOCK_COMP:
> +	case KVM_S390_INT_CPU_TIMER:
> +		break;
> +	default:
> +		return -EINVAL;
>  	}
>  	return 0;
>  }
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index f329dcb3f44c..082eac2abc88 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -4323,7 +4323,7 @@ long kvm_arch_vcpu_async_ioctl(struct file *filp,
>  	}
>  	case KVM_S390_INTERRUPT: {
>  		struct kvm_s390_interrupt s390int;
> -		struct kvm_s390_irq s390irq;
> +		struct kvm_s390_irq s390irq = {};
>  
>  		if (copy_from_user(&s390int, argp, sizeof(s390int)))
>  			return -EFAULT;
>