# Re: \[RFC PATCH for 4.21 06/16\] cpu\_opv: Provide cpu\_opv system call (v8)

- From: Sergey Senozhatsky \<hidden\>
- Date: 2018-10-16 08:10:37 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2018/10/5409055
- Thread: https://ratatoskr.run/linux-api/2018/10/5404697/t.md

```text
Hi Mathieu,

On (10/10/18 15:19), Mathieu Desnoyers wrote:
[..]
> +SYSCALL_DEFINE4(cpu_opv, struct cpu_op __user *, ucpuopv, int, cpuopcnt,
> +		int, cpu, int, flags)
> +{
[..]
> +again:
> +	ret = cpu_opv_pin_pages(cpuopv, cpuopcnt, &vaddr_ptrs);
> +	if (ret)
> +		goto end;
> +	ret = do_cpu_opv(cpuopv, cpuopcnt, &vaddr_ptrs, cpu);
> +	if (ret == -EAGAIN)
> +		retry = true;
> +end:
> +	for (i = 0; i < vaddr_ptrs.nr_vaddr; i++) {
> +		struct vaddr *vaddr = &vaddr_ptrs.addr[i];
> +		int j;
> +
> +		vm_unmap_user_ram((void *)vaddr->mem, vaddr->nr_pages);

A dumb question.

Both vm_unmap_user_ram() and vm_map_user_ram() can BUG_ON().
So this is
   userspace -> syscall -> cpu_opv() -> vm_unmap_user_ram() -> BUG_ON()

Any chance someone can exploit it?

	-ss
```