Re: [PATCH 1/2] KVM: s390: Limit adapter indicator access to mapped page

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Tue, 17 Feb 2026 09:54:22 +0100
Janosch Frank <frankja@linux.ibm.com> wrote:

> While we check the address for errors, we don't seem to check the bit
> offsets and since they are 32 and 64 bits a lot of memory can be
> reached indirectly via those offsets.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> Fixes: 84223598778b ("KVM: s390: irq routing for adapter interrupts.")

Suggested-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reported-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

:)

> ---
>  arch/s390/kvm/interrupt.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index 1c2bb5cd7e12..cd4851e33a5b 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -2724,6 +2724,9 @@ static unsigned long get_ind_bit(__u64 addr, unsigned long bit_nr, bool swap)
>  
>  	bit = bit_nr + (addr % PAGE_SIZE) * 8;
>  
> +	/* kvm_set_routing_entry() should never allow this to happen */
> +	WARN_ON_ONCE(bit > (PAGE_SIZE * BITS_PER_BYTE - 1));
> +
>  	return swap ? (bit ^ (BITS_PER_LONG - 1)) : bit;
>  }
>  
> @@ -2852,6 +2855,7 @@ int kvm_set_routing_entry(struct kvm *kvm,
>  			  struct kvm_kernel_irq_routing_entry *e,
>  			  const struct kvm_irq_routing_entry *ue)
>  {
> +	const struct kvm_irq_routing_s390_adapter *adapter;
>  	u64 uaddr_s, uaddr_i;
>  	int idx;
>  
> @@ -2862,6 +2866,14 @@ int kvm_set_routing_entry(struct kvm *kvm,
>  			return -EINVAL;
>  		e->set = set_adapter_int;
>  
> +		adapter = &ue->u.adapter;
> +		if (adapter->summary_addr + BITS_TO_BYTES(adapter->summary_offset) >=
> +		    (adapter->summary_addr & PAGE_MASK) + PAGE_SIZE)
> +			return -EINVAL;
> +		if (adapter->ind_addr + BITS_TO_BYTES(adapter->ind_offset) >=
> +		    (adapter->ind_addr & PAGE_MASK) + PAGE_SIZE)
> +			return -EINVAL;
> +
>  		idx = srcu_read_lock(&kvm->srcu);
>  		uaddr_s = gpa_to_hva(kvm, ue->u.adapter.summary_addr);
>  		uaddr_i = gpa_to_hva(kvm, ue->u.adapter.ind_addr);