# Re: \[PATCH\] vsprintf: Do not break early boot with probing addresses

- From: Steven Rostedt \<rostedt@goodmis.org\>
- Date: 2019-05-10 16:41:02 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2019/05/5594202
- Thread: https://ratatoskr.run/linuxppc-dev/2019/05/5592853/t.md

```text
On Fri, 10 May 2019 18:32:58 +0200
Martin Schwidefsky [ref] wrote:

> On Fri, 10 May 2019 12:24:01 -0400
> Steven Rostedt [ref] wrote:
> 
> > On Fri, 10 May 2019 10:42:13 +0200
> > Petr Mladek [ref] wrote:
> >   
> > >  static const char *check_pointer_msg(const void *ptr)
> > >  {
> > > -	char byte;
> > > -
> > >  	if (!ptr)
> > >  		return "(null)";
> > >  
> > > -	if (probe_kernel_address(ptr, byte))
> > > +	if ((unsigned long)ptr < PAGE_SIZE || IS_ERR_VALUE(ptr))
> > >  		return "(efault)";
> > >      
> > 
> > 
> > 	< PAGE_SIZE ?
> > 
> > do you mean: < TASK_SIZE ?  
> 
> The check with < TASK_SIZE would break on s390. The 'ptr' is
> in the kernel address space, *not* in the user address space.
> Remember s390 has two separate address spaces for kernel/user
> the check < TASK_SIZE only makes sense with a __user pointer.
> 

So we allow this to read user addresses? Can't that cause a fault?

If the condition is true, we return "(efault)".

-- Steve
```