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

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Message-ID: <20250513142113.GA9443@willie-the-truck>
Date: Tue, 13 May 2025 15:21:14 +0100
From: Will Deacon <will@...nel.org>
To: perlarsen@...gle.com
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Sudeep Holla <sudeep.holla@....com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, sebastianene@...gle.com,
	lpieralisi@...nel.org, arve@...roid.com, qwandor@...gle.com,
	kernel-team@...roid.com, armellel@...gle.com, perl@...unant.com,
	jean-philippe@...aro.org, ahomescu@...gle.com, tabba@...gle.com,
	qperret@...gle.com, james.morse@....com
Subject: Re: [PATCH v3 1/3] KVM: arm64: Restrict FF-A host version
 renegotiation

On Tue, May 13, 2025 at 06:28:30AM +0000, Per Larsen via B4 Relay wrote:
> From: Per Larsen <perlarsen@...gle.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@...gle.com>
> Signed-off-by: Per Larsen <perl@...unant.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@...nel.org>

Will