[PATCH v3 1/3] KVM: arm64: Restrict FF-A host version renegotiation

[Will Deacon]

On Tue, May 13, 2025 at 06:28:30AM +0000, Per Larsen via B4 Relay wrote:
> From: Per Larsen <perlarsen at google.com>
> 
> Prevent the host from re-negotiating a lesser minor version with the
> hypervisor. Once the hypervisor negotiates a version, that should
> remain locked in. Fix the current behaviour by returning NOT_SUPPORTED
> to avoid the FF-A interoperability rules with lesser minor versions that
> allow the host version to downgrade.
> 
> Signed-off-by: Per Larsen <perlarsen at google.com>
> Signed-off-by: Per Larsen <perl at immunant.com>

I'm not entirely sure why we need two SoB lines here...

>  arch/arm64/kvm/hyp/nvhe/ffa.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index 3369dd0c4009f84ad3cf9481c747bdc57a162370..2c199d40811efb5bfae199c4a67d8ae3d9307357 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> @@ -712,7 +712,10 @@ static void do_ffa_version(struct arm_smccc_res *res,
>  
>  	hyp_spin_lock(&version_lock);
>  	if (has_version_negotiated) {
> -		res->a0 = hyp_ffa_version;
> +		if (FFA_MINOR_VERSION(ffa_req_version) < FFA_MINOR_VERSION(hyp_ffa_version))
> +			res->a0 = FFA_RET_NOT_SUPPORTED;
> +		else
> +			res->a0 = hyp_ffa_version;
>  		goto unlock;

... but the patch looks fine to me.

Acked-by: Will Deacon <will at kernel.org>

Will