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Date: Mon, 13 May 2019 12:13:20 +0300
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: Re: [PATCH] vsprintf: Do not break early boot with probing addresses
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To: David Laight <David.Laight@ACULAB.COM>
Cc: 'christophe leroy' <christophe.leroy@c-s.fr>, Steven Rostedt <rostedt@goodmis.org>, Petr Mladek <pmladek@suse.com>, Linus Torvalds <torvalds@linux-foundation.org>, 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" <linux-kernel@vger.kernel.org>, Michael Ellerman <mpe@ellerman.id.au>, "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>, Russell Currey <ruscur@russell.cc>, Stephen Rothwell <sfr@ozlabs.org>, Heiko Carstens <heiko.carstens@de.ibm.com>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, "linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>
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On Mon, May 13, 2019 at 08:52:41AM +0000, David Laight wrote:
> From: christophe leroy
> > Sent: 10 May 2019 18:35
> > Le 10/05/2019 =E0 18:24, Steven Rostedt a =E9crit=A0:
> > > On Fri, 10 May 2019 10:42:13 +0200
> > > Petr Mladek <pmladek@suse.com> wrote:

> > >> -	if (probe_kernel_address(ptr, byte))
> > >> +	if ((unsigned long)ptr < PAGE_SIZE || IS_ERR_VALUE(ptr))
> > >>   		return "(efault)";
>=20
> "efault" looks a bit like a spellling mistake for "default".

It's a special, thus it's in parenthesis, though somebody can be
misguided.

> > Usually, < PAGE_SIZE means NULL pointer dereference (via the member of a
> > struct)
>=20
> Maybe the caller should pass in a short buffer so that you can return
> "(err-%d)"
> or "(null+%#x)" ?

In both cases it should be limited to the size of pointer (8 or 16
characters). Something like "(e:%4d)" would work for error codes.

The "(null)" is good enough by itself and already an established
practice..

--=20
With Best Regards,
Andy Shevchenko