Re: [PATCH v6 25/43] arm64: Don't expose stolen time for realm guests

[Gavin Shan]

On 12/13/24 1:55 AM, Steven Price wrote:
> It doesn't make much sense as a realm guest wouldn't want to trust the
> host. It will also need some extra work to ensure that KVM will only
> attempt to write into a shared memory region. So for now just disable
> it.
>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> ---
>   arch/arm64/kvm/arm.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index eff1a4ec892b..134acb4ee26f 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -432,7 +432,10 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   		r = system_supports_mte();
>   		break;
>   	case KVM_CAP_STEAL_TIME:
> -		r = kvm_arm_pvtime_supported();
> +		if (kvm_is_realm(kvm))
> +			r = 0;
> +		else
> +			r = kvm_arm_pvtime_supported();
>   		break;

kvm_vm_ioctl_check_extension() can be called on the file descriptor of "/dev/kvm".
'kvm' is NULL and kvm_is_realm() returns false, which is the missed corner case.

>   	case KVM_CAP_ARM_EL1_32BIT:
>   		r = cpus_have_final_cap(ARM64_HAS_32BIT_EL1);

Thanks,
Gavin