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Date: Fri, 10 May 2019 18:32:58 +0200
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
Subject: Re: [PATCH] vsprintf: Do not break early boot with probing
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To: Steven Rostedt <rostedt@goodmis.org>
Cc: Petr Mladek <pmladek@suse.com>, Linus Torvalds <torvalds@linux-foundation.org>, Andy Shevchenko <andriy.shevchenko@linux.intel.com>, Rasmus Villemoes <linux@rasmusvillemoes.dk>, "Tobin C . Harding" <me@tobin.cc>, Michal Hocko <mhocko@suse.cz>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, linux-kernel@vger.kernel.org, Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@lists.ozlabs.org, Russell Currey <ruscur@russell.cc>, Christophe Leroy <christophe.leroy@c-s.fr>, Stephen Rothwell <sfr@ozlabs.org>, Heiko Carstens <heiko.carstens@de.ibm.com>, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org
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On Fri, 10 May 2019 12:24:01 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 10 May 2019 10:42:13 +0200
> Petr Mladek <pmladek@suse.com> 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.