KVM: s390: fix memory overwrites when not using SCA entries

davidhildenbrand · borntraeger · commit f07afa0462b7 · 2018-03-06T13:33:02.000Z
Even if we don't have extended SCA support, we can have more than 64 CPUs if we don't enable any HW features that might use the SCA entries. Now, this works just fine, but we missed a return, which is why we would actually store the SCA entries. If we have more than 64 CPUs, this means writing outside of the basic SCA - bad. Let's fix this. This allows > 64 CPUs when running nested (under vSIE) without random crashes. Fixes: a694067 ("KVM: s390: allow 255 VCPUs when sca entries aren't used") Reported-by: Christian Borntraeger <borntraeger@de.ibm.com> Tested-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: David Hildenbrand <david@redhat.com> Message-Id: <20180306132758.21034-1-david@redhat.com> Cc: stable@vger.kernel.org Reviewed-by: Cornelia Huck <cohuck@redhat.com> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
@@ -2147,6 +2147,7 @@ static void sca_add_vcpu(struct kvm_vcpu *vcpu)
 		/* we still need the basic sca for the ipte control */
 		vcpu->arch.sie_block->scaoh = (__u32)(((__u64)sca) >> 32);
 		vcpu->arch.sie_block->scaol = (__u32)(__u64)sca;
+		return;
 	}
 	read_lock(&vcpu->kvm->arch.sca_lock);
 	if (vcpu->kvm->arch.use_esca) {

Original file line number	Diff line number	Diff line change
`@@ -2147,6 +2147,7 @@ static void sca_add_vcpu(struct kvm_vcpu *vcpu)`
`2147`	`2147`	`/* we still need the basic sca for the ipte control */`
`2148`	`2148`	`vcpu->arch.sie_block->scaoh = (__u32)(((__u64)sca) >> 32);`
`2149`	`2149`	`vcpu->arch.sie_block->scaol = (__u32)(__u64)sca;`
	`2150`	`+ return;`
`2150`	`2151`	`}`
`2151`	`2152`	`read_lock(&vcpu->kvm->arch.sca_lock);`
`2152`	`2153`	`if (vcpu->kvm->arch.use_esca) {`