KVM: s390: Harden copying of userspace-array against overflow

guestdbg.c utilizes memdup_user() to copy a userspace array. This,
currently, does not check for an overflow.

Use the new wrapper memdup_array_user() to copy the array more safely.

Note, KVM explicitly checks the number of entries before duplicating the
array, i.e. adding the overflow check should be a glorified nop.

Suggested-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Link: https://lore.kernel.org/r/20231102181526.43279-3-pstanner@redhat.com
[sean: call out that KVM pre-checks the number of entries]
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: Philipp Stanner

arch/s390/kvm/guestdbg.c

@@ -213,8 +213,8 @@ int kvm_s390_import_bp_data(struct kvm_vcpu *vcpu,
 	else if (dbg->arch.nr_hw_bp > MAX_BP_COUNT)
 		return -EINVAL;
 
-	bp_data = memdup_user(dbg->arch.hw_bp,
-			      sizeof(*bp_data) * dbg->arch.nr_hw_bp);
+	bp_data = memdup_array_user(dbg->arch.hw_bp, dbg->arch.nr_hw_bp,
+				    sizeof(*bp_data));
 	if (IS_ERR(bp_data))
 		return PTR_ERR(bp_data);