[PATCH 1/4] KVM: arm64: Trap FFA_VERSION host call in pKVM

[Sebastian Ene]

The pKVM hypervisor initializes with FF-A version 1.0. Keep the
supported version inside the host structure and prevent the host
drivers from overwriting the FF-A version with an increased version.
Without trapping the call, the host drivers can negotiate a higher
version number with TEE which can result in a different memory layout
described during the memory sharing calls.

Signed-off-by: Sebastian Ene <sebastianene at google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 43 ++++++++++++++++++++++++++++++++---
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 320f2eaa14a9..023712e8beeb 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -58,6 +58,7 @@ struct kvm_ffa_buffers {
 	hyp_spinlock_t lock;
 	void *tx;
 	void *rx;
+	u32 ffa_version;
 };
 
 /*
@@ -640,6 +641,39 @@ static bool do_ffa_features(struct arm_smccc_res *res,
 	return true;
 }
 
+static void do_ffa_version(struct arm_smccc_res *res,
+			   struct kvm_cpu_context *ctxt)
+{
+	DECLARE_REG(u32, ffa_req_version, ctxt, 1);
+	u32 current_version;
+
+	hyp_spin_lock(&host_buffers.lock);
+	current_version = host_buffers.ffa_version;
+	if (FFA_MAJOR_VERSION(ffa_req_version) != FFA_MAJOR_VERSION(current_version)) {
+		res->a0 = FFA_RET_NOT_SUPPORTED;
+		goto unlock;
+	}
+
+	/*
+	 * If the client driver tries to downgrade the version, we need to ask
+	 * first if TEE supports it.
+	 */
+	if (FFA_MINOR_VERSION(ffa_req_version) < FFA_MINOR_VERSION(current_version)) {
+		arm_smccc_1_1_smc(FFA_VERSION, ffa_req_version, 0,
+				  0, 0, 0, 0, 0,
+				  res);
+		if (res->a0 == FFA_RET_NOT_SUPPORTED)
+			goto unlock;
+
+		host_buffers.ffa_version = ffa_req_version;
+		goto unlock;
+	}
+
+	res->a0 = current_version;
+unlock:
+	hyp_spin_unlock(&host_buffers.lock);
+}
+
 bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 {
 	struct arm_smccc_res res;
@@ -686,6 +720,9 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
 	case FFA_MEM_FRAG_TX:
 		do_ffa_mem_frag_tx(&res, host_ctxt);
 		goto out_handled;
+	case FFA_VERSION:
+		do_ffa_version(&res, host_ctxt);
+		goto out_handled;
 	}
 
 	if (ffa_call_supported(func_id))
@@ -726,6 +763,8 @@ int hyp_ffa_init(void *pages)
 	if (FFA_MAJOR_VERSION(res.a0) != 1)
 		return -EOPNOTSUPP;
 
+	host_buffers.ffa_version = res.a0;
+
 	arm_smccc_1_1_smc(FFA_ID_GET, 0, 0, 0, 0, 0, 0, 0, &res);
 	if (res.a0 != FFA_SUCCESS)
 		return -EOPNOTSUPP;
@@ -772,9 +811,7 @@ int hyp_ffa_init(void *pages)
 		.rx	= rx,
 	};
 
-	host_buffers = (struct kvm_ffa_buffers) {
-		.lock	= __HYP_SPIN_LOCK_UNLOCKED,
-	};
+	host_buffers.lock = __HYP_SPIN_LOCK_UNLOCKED;
 
 	return 0;
 }
-- 
2.44.0.769.g3c40516874-goog