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

From: Martin Schwidefsky <[email-masked]>
Date: Fri, 10 May 2019 18:32:58 +0200

On Fri, 10 May 2019 12:24:01 -0400
Steven Rostedt <[email-masked]> wrote:

> On Fri, 10 May 2019 10:42:13 +0200
> Petr Mladek <[email-masked]> 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.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.