Re: [PATCH 2/4] KVM: s390: vsie: zero stale crypto bits

On Tue, 11 Aug 2026 17:37:36 +0200
Christian Borntraeger <[email protected]> wrote:

> When shadowing crypto access bits from a format0 apcb (crycb 0 or 1),
> the bits 64..255 are unchanged from whatever is in the vsie page in the
> crycb and thus in the apcb. This gives a nested guest potential access
> to a device no longer available. Zero out the remaining bits.
> 
> Fixes: 6b79de4b056e ("KVM: s390: vsie: allow guest FORMAT-1 CRYCB on host FORMAT-2")
> Cc: [email protected]
> Signed-off-by: Christian Borntraeger <[email protected]>

Reviewed-by: Claudio Imbrenda <[email protected]>

> ---
>  arch/s390/kvm/vsie.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index f546239d8ff8..7971947d2fe5 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -172,6 +172,7 @@ static int setup_apcb10(struct kvm_vcpu *vcpu, struct kvm_s390_apcb1 *apcb_s,
>  			    sizeof(struct kvm_s390_apcb0)))
>  		return -EFAULT;
>  
> +	memset(apcb_s, 0, sizeof(*apcb_s));
>  	apcb_s->apm[0] = apcb_h->apm[0] & tmp.apm[0];
>  	apcb_s->aqm[0] = apcb_h->aqm[0] & tmp.aqm[0] & 0xffff000000000000UL;
>  	apcb_s->adm[0] = apcb_h->adm[0] & tmp.adm[0] & 0xffff000000000000UL;