Re: [PATCH v7 4/7] KVM: arm64: Support FFA_NOTIFICATION_SET in host handler

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Incomplete validation of MBZ bits in the `FFA_NOTIFICATION_SET` flags parameter.
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commit 143dce86ae3c0640e01881b137e64cf1efebff28
Author: Sebastian Ene <sebastianene@google.com>

KVM: arm64: Support FFA_NOTIFICATION_SET in host handler

This commit allows FF-A notification SET messages to be proxied from the
pKVM hypervisor to Trustzone by validating the endpoint ID and flags arguments
before forwarding the hypercall.

> diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> index d52d7c4d5e7f5..2bb16aa414f9f 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c

[ ... ]

> @@ -917,6 +917,27 @@ static void do_ffa_notif_unbind(struct arm_smccc_1_2_regs *res,
>  	hyp_smccc_1_2_smc(args, res);
>  }
>  
> +static void do_ffa_notif_set(struct arm_smccc_1_2_regs *res,
> +			     struct kvm_cpu_context *ctxt)
> +{
> +	DECLARE_REG(u32, endp_id, ctxt, 1);
> +	DECLARE_REG(u32, flags, ctxt, 2);
> +	struct arm_smccc_1_2_regs *args;
> +
> +	if (FIELD_GET(FFA_NOTIF_SENDER_ENDP_MASK, endp_id) != HOST_FFA_ID) {
> +		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
> +		return;
> +	}
> +
> +	if (flags & GENMASK(15, 2)) {

[Severity: Medium]
Does this missing validation allow the host to pass arbitrary data in the
upper bits of the flags parameter to EL3?

In do_ffa_notif_set(), the check masks and verifies only bits 15:2. However,
the FF-A specification defines bits 31:16 as Must Be Zero (MBZ) as well.

This seems to introduce a regression where pKVM does not completely sanitize
host inputs before forwarding them to TrustZone, potentially exposing EL3
to unauthorized use of future extensions.

> +		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
> +		return;
> +	}
> +
> +	args = (void *)&ctxt->regs.regs[0];
> +	hyp_smccc_1_2_smc(args, res);
> +}
> +

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260629093558.2425257-1-sebastianene@google.com?part=4