Re: [PATCH v6 7/7] KVM: arm64: Enforce strict SBZ checks in the FF-A proxy

[Will Deacon]

On Fri, Jun 26, 2026 at 07:45:45AM +0000, Sebastian Ene wrote:
> Introduce a helper method ffa_check_unused_args_sbz to enforce strict
> arguments checking when the hypervisor acts as a relayer between the
> host and Trustzone.
> 
> Signed-off-by: Sebastian Ene <sebastianene@xxxxxxxxxx>
> Reviewed-by: Vincent Donnefort <vdonnefort@xxxxxxxxxx>
> ---
>  arch/arm64/kvm/hyp/nvhe/ffa.c | 96 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 95 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index 712811e89435..bd50ddc5b61c 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -74,6 +74,21 @@ static u32 hyp_ffa_version;
>  static bool has_version_negotiated;
>  static hyp_spinlock_t version_lock;
>  
> +static bool ffa_check_unused_args_sbz(struct kvm_cpu_context *ctxt, int first_reg)
> +{
> +	DECLARE_REG(u32, func_id, ctxt, 0);
> +	int reg, end_reg = 7;
> +
> +	if (FFA_MINOR_VERSION(hyp_ffa_version) >= 2)
> +		end_reg = ARM_SMCCC_IS_64(func_id) ? 17 : 7;

This looks like an accident waiting to happen if we don't check the major
number as well.

I think you should just check:

	if (hyp_ffa_version >= FFA_VERSION_1_2)

instead.

You should also add a comment.

Will