linux-kernel - Re: [PATCH] s390/kvm: Reject memory region operations for ucontrol VMs

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Date: Mon, 24 Jun 2024 17:33:21 +0200
From: Claudio Imbrenda <imbrenda@...ux.ibm.com>
To: Christoph Schlameuss <schlameuss@...ux.ibm.com>
Cc: linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Christian Borntraeger
 <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David
 Hildenbrand <david@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH] s390/kvm: Reject memory region operations for ucontrol
 VMs

On Mon, 24 Jun 2024 11:59:02 +0200
Christoph Schlameuss <schlameuss@...ux.ibm.com> wrote:

> This change rejects the KVM_SET_USER_MEMORY_REGION and
> KVM_SET_USER_MEMORY_REGION2 ioctls when called on a ucontrol VM.
> This is neccessary since ucontrol VMs have kvm->arch.gmap set to 0 and
> would thus result in a null pointer dereference further in.
> Memory management needs to be performed in userspace and using the
> ioctls KVM_S390_UCAS_MAP and KVM_S390_UCAS_UNMAP.
> 
> Also improve s390 specific documentation for KVM_SET_USER_MEMORY_REGION
> and KVM_SET_USER_MEMORY_REGION2.
> 
> Signed-off-by: Christoph Schlameuss <schlameuss@...ux.ibm.com>

Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>

> ---
>  Documentation/virt/kvm/api.rst | 12 ++++++++++++
>  arch/s390/kvm/kvm-s390.c       |  3 +++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index a71d91978d9e..eec8df1dde06 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -1403,6 +1403,12 @@ Instead, an abort (data abort if the cause of the page-table update
>  was a load or a store, instruction abort if it was an instruction
>  fetch) is injected in the guest.
>  
> +S390:
> +^^^^^
> +
> +Returns -EINVAL if the VM has the KVM_VM_S390_UCONTROL flag set.
> +Returns -EINVAL if called on a protected VM.
> +
>  4.36 KVM_SET_TSS_ADDR
>  ---------------------
>  
> @@ -6273,6 +6279,12 @@ state.  At VM creation time, all memory is shared, i.e. the PRIVATE attribute
>  is '0' for all gfns.  Userspace can control whether memory is shared/private by
>  toggling KVM_MEMORY_ATTRIBUTE_PRIVATE via KVM_SET_MEMORY_ATTRIBUTES as needed.
>  
> +S390:
> +^^^^^
> +
> +Returns -EINVAL if the VM has the KVM_VM_S390_UCONTROL flag set.
> +Returns -EINVAL if called on a protected VM.
> +
>  4.141 KVM_SET_MEMORY_ATTRIBUTES
>  -------------------------------
>  
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 82e9631cd9ef..854d0d1410be 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -5748,6 +5748,9 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  {
>  	gpa_t size;
>  
> +	if (kvm_is_ucontrol(kvm))
> +		return -EINVAL;
> +
>  	/* When we are protected, we should not change the memory slots */
>  	if (kvm_s390_pv_get_handle(kvm))
>  		return -EINVAL;
> 
> base-commit: f2661062f16b2de5d7b6a5c42a9a5c96326b8454