[PATCH v2 8/8] KVM: s390: Prevent memslots outside the ASCE range

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

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@linux.ibm.com>
---
 arch/s390/kvm/kvm-s390.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index e09960c2e6ed..1796a7c645a9 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -999,7 +999,10 @@ static int kvm_s390_set_mem_control(struct kvm *kvm, struct kvm_device_attr *att
 		break;
 	}
 	case KVM_S390_VM_MEM_LIMIT_SIZE: {
+		struct kvm_memslots *slots;
+		struct kvm_memory_slot *ms;
 		unsigned long new_limit;
+		int bkt;
 
 		if (kvm_is_ucontrol(kvm))
 			return -EINVAL;
@@ -1007,6 +1010,8 @@ static int kvm_s390_set_mem_control(struct kvm *kvm, struct kvm_device_attr *att
 		if (get_user(new_limit, (u64 __user *)attr->addr))
 			return -EFAULT;
 
+		guard(mutex)(&kvm->lock);
+
 		if (kvm->arch.mem_limit != KVM_S390_NO_MEM_LIMIT &&
 		    new_limit > kvm->arch.mem_limit)
 			return -E2BIG;
@@ -1014,12 +1019,27 @@ static int kvm_s390_set_mem_control(struct kvm *kvm, struct kvm_device_attr *att
 		if (!new_limit)
 			return -EINVAL;
 
-		ret = -EBUSY;
-		if (!kvm->created_vcpus)
+		if (kvm->created_vcpus)
+			return -EBUSY;
+
+		ret = 0;
+		scoped_guard(mutex, &kvm->slots_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));
+		if (ret)
+			break;
 		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);
+		VM_EVENT(kvm, 3, "New guest asce: 0x%p", (void *)kvm->arch.gmap->asce.val);
 		break;
 	}
 	default:
@@ -5672,6 +5692,8 @@ 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