Re: [PATCH] KVM: arm64: Don't WARN on an unknown VM ioctl in protected mode

[Suzuki K Poulose]

On 14/09/2026 10:38, Fuad Tabba wrote:
> kvm_pkvm_ioctl_allowed() WARNs when kvm_get_cap_for_kvm_ioctl() doesn't
> find the ioctl number in vm_ioctl_caps[], and kvm_arch_vm_ioctl() calls
> it for every number the generic code doesn't handle, so
> ioctl(vm_fd, 0xdeadbeef) from userspace taints a pKVM host and panics it
> under panic_on_warn. The lookup is fed userspace input: return false,
> and userspace gets the -EINVAL kvm_arch_vm_ioctl() returns for that
> number on a host without pKVM.
>
> Fixes: b12b3b04f6ba0 ("KVM: arm64: Check whether a VM IOCTL is allowed in pKVM")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Fuad Tabba <fuad.tabba@xxxxxxxxx>

I hit this myself ;-) and had a patch in my series. Thanks for posting
this

Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

> ---
>   arch/arm64/include/asm/kvm_pkvm.h | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_pkvm.h b/arch/arm64/include/asm/kvm_pkvm.h
> index beea00e693a0a..cad60569f0619 100644
> --- a/arch/arm64/include/asm/kvm_pkvm.h
> +++ b/arch/arm64/include/asm/kvm_pkvm.h
> @@ -65,8 +65,7 @@ static inline bool kvm_pkvm_ioctl_allowed(struct kvm *kvm, unsigned int ioctl)
>   	int r;
>   
>   	r = kvm_get_cap_for_kvm_ioctl(ioctl, &ext);
> -
> -	if (WARN_ON_ONCE(r < 0))
> +	if (r < 0)
>   		return false;
>   
>   	return kvm_pkvm_ext_allowed(kvm, ext);