[PATCH v5 04/13] KVM: s390: ucontrol: Fix sca_clear_ext_call()

[Claudio Imbrenda]

When cleaning up a UCONTROL VM, sca_clear_ext_call() will touch memory
outside of the allocated ESCA block, and UCONTROL VMs don't even use
ESCA.

Fix by not touching ESCA for UCONTROL VMs.

Opportunistically add checks in sca_ext_call_pending() and
sca_inject_ext_call() to make sure UCONTROL VMs won't call those
functions.

Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Fixes: 7d43bafcff17 ("KVM: s390: Make provisions for ESCA utilization")
---
 arch/s390/kvm/interrupt.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 2acdff130fa6..d02724bd1829 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -50,6 +50,8 @@ static int sca_ext_call_pending(struct kvm_vcpu *vcpu, int *src_id)
 	if (!kvm_s390_test_cpuflags(vcpu, CPUSTAT_ECALL_PEND))
 		return 0;
 
+	if (KVM_BUG_ON(kvm_is_ucontrol(vcpu->kvm), vcpu->kvm))
+		return -EINVAL;
 	BUG_ON(!kvm_s390_use_sca_entries());
 
 	if (src_id)
@@ -66,6 +68,8 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
 	int expect, rc;
 
 	BUG_ON(!kvm_s390_use_sca_entries());
+	if (KVM_BUG_ON(kvm_is_ucontrol(vcpu->kvm), vcpu->kvm))
+		return -EINVAL;
 
 	old_val = READ_ONCE(*sigp_ctrl);
 	old_val.c = 0;
@@ -84,10 +88,13 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
 static void sca_clear_ext_call(struct kvm_vcpu *vcpu)
 {
 	struct esca_block *sca = vcpu->kvm->arch.sca;
-	union esca_sigp_ctrl *sigp_ctrl = &sca->cpu[vcpu->vcpu_id].sigp_ctrl;
+	union esca_sigp_ctrl *sigp_ctrl;
 
-	if (!kvm_s390_use_sca_entries() || !vcpu->arch.initialized)
+	if (!kvm_s390_use_sca_entries() || !vcpu->arch.initialized || kvm_is_ucontrol(vcpu->kvm))
 		return;
+
+	/* Initialize after the above check, to prevent going out of bounds */
+	sigp_ctrl = &sca->cpu[vcpu->vcpu_id].sigp_ctrl;
 	kvm_s390_clear_cpuflags(vcpu, CPUSTAT_ECALL_PEND);
 
 	WRITE_ONCE(sigp_ctrl->value, 0);
-- 
2.55.0