linux-kernel - [PATCH v2 1/3] KVM: arm64: Restrict FF-A host version renegotiation

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Message-Id: <20250508-virtio-msg-ffa-v2-1-ed84f8053965@google.com>
Date: Thu, 08 May 2025 08:38:52 +0000
From: Per Larsen via B4 Relay <devnull+perlarsen.google.com@...nel.org>
To: 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>, Will Deacon <will@...nel.org>, 
 Sudeep Holla <sudeep.holla@....com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, arve@...roid.com, lpieralisi@...nel.org, 
 qwandor@...gle.com, jean-philippe@...aro.org, james.morse@....com, 
 perl@...unant.com, tabba@...gle.com, kernel-team@...roid.com, 
 armellel@...gle.com, qperret@...gle.com, sebastianene@...gle.com, 
 ahomescu@...gle.com, Per Larsen <perlarsen@...gle.com>
Subject: [PATCH v2 1/3] KVM: arm64: Restrict FF-A host version
 renegotiation

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>
---
 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;
 	}
 

-- 
2.49.0.987.g0cc8ee98dc-goog