[PATCH v1 7/7] KVM: s390: Prevent memslots outside the ASCE range

[Claudio Imbrenda]

With KVM_S390_VM_MEM_LIMIT_SIZE, userspace can set the highest address
allowed for the VM. Creating a memslot that lies over the maximum
address does not make sense and is only a potential source of bugs.

Prevent creation of memslots over the maximum address, and prevent the
maximum address from being reduced below the end of existing memslots.

Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
---
 arch/s390/kvm/kvm-s390.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index e09960c2e6ed..875f6e2a4a52 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1015,8 +1015,26 @@ static int kvm_s390_set_mem_control(struct kvm *kvm, struct kvm_device_attr *att
 			return -EINVAL;
 
 		ret = -EBUSY;
-		if (!kvm->created_vcpus)
-			ret = gmap_set_limit(kvm->arch.gmap, gpa_to_gfn(new_limit));
+		if (!kvm->created_vcpus) {
+			struct kvm_memslots *slots;
+			struct kvm_memory_slot *ms;
+			int bkt;
+
+			ret = 0;
+			mutex_lock(&kvm->slots_arch_lock);
+			slots = kvm_memslots(kvm);
+			if (slots && !kvm_memslots_empty(slots)) {
+				kvm_for_each_memslot(ms, bkt, slots) {
+					if (gpa_to_gfn(new_limit) < ms->base_gfn + ms->npages) {
+						ret = -EBUSY;
+						break;
+					}
+				}
+			}
+			if (!ret)
+				ret = gmap_set_limit(kvm->arch.gmap, gpa_to_gfn(new_limit));
+			mutex_unlock(&kvm->slots_arch_lock);
+		}
 		VM_EVENT(kvm, 3, "SET: max guest address: %lu", new_limit);
 		VM_EVENT(kvm, 3, "New guest asce: 0x%p",
 			 (void *)kvm->arch.gmap->asce.val);
@@ -5672,6 +5690,8 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 			return -EINVAL;
 		if ((new->base_gfn + new->npages) * PAGE_SIZE > kvm->arch.mem_limit)
 			return -EINVAL;
+		if (!asce_contains_gfn(kvm->arch.gmap->asce, new->base_gfn + new->npages - 1))
+			return -EINVAL;
 	}
 
 	if (!kvm->arch.migration_mode)
-- 
2.54.0