Avoid locking, manipulating vm_map for bogus address lookup

[dougm]

Summary

vm_map_lookup is sometimes called with a vaddr argument outside the bounds of the vm_map. Detect that, and return KERN_INVALID_ADDRESS, without locking and altering the map.

[dougm]

alc has demanded evidence that this test will be triggered in enough cases to justify its cost, so it will sit here until I can present such evidence.