linux-kernel - Re: [PATCH] vsprintf: Do not break early boot with probing addresses

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Message-ID: <20190513091320.GK9224@smile.fi.intel.com>
Date:   Mon, 13 May 2019 12:13:20 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'christophe leroy' <christophe.leroy@....fr>,
        Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Tobin C . Harding" <me@...in.cc>, Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Russell Currey <ruscur@...sell.cc>,
        Stephen Rothwell <sfr@...abs.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH] vsprintf: Do not break early boot with probing addresses

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 à 18:24, Steven Rostedt a écrit :
> > > On Fri, 10 May 2019 10:42:13 +0200
> > > Petr Mladek <pmladek@...e.com> wrote:

> > >> -	if (probe_kernel_address(ptr, byte))
> > >> +	if ((unsigned long)ptr < PAGE_SIZE || IS_ERR_VALUE(ptr))
> > >>   		return "(efault)";
> 
> "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)
> 
> 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..

-- 
With Best Regards,
Andy Shevchenko