We present LLVM/Offload Sanitizer, an address sanitizer (ASAN) designed for GPUs. In contrast to the classic CPU ASAN, the offload sanitizer will avoids high memory overhead, and even memory traffic, via software managed virtual memory. Allocations result in "virtual pointers" that are checked and translated prior to accesses but without buffer zones and, in case of shared and local GPU memory, even without additional memory traffic. Our performance results show huge advantages against the classic CPU design ported to the GPU, however, we will details various pitfalls that make efficient sanitization of GPU code especially hard. Finally, we will show some initial comparison of this design against classic ASAN on the CPU.