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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 15 May 2019 09:23:05 +0200
Message-ID: <CAMuHMdUFEwxwQUWg0HNUiz75hP6S7TVGSx7fWXnsQ_3qsVfotQ@mail.gmail.com>
Subject: Re: [PATCH] vsprintf: Do not break early boot with probing addresses
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     David Laight <David.Laight@aculab.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Petr Mladek <pmladek@suse.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        christophe leroy <christophe.leroy@c-s.fr>,
        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>,
        "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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Hi Steve,

On Tue, May 14, 2019 at 9:35 PM Steven Rostedt <rostedt@goodmis.org> wrote:
> On Tue, 14 May 2019 21:13:06 +0200
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > > Do we care about the value? "(-E%u)"?
> > >
> > > That too could be confusing. What would (-E22) be considered by a user
> > > doing an sprintf() on some string. I know that would confuse me, or I
> > > would think that it was what the %pX displayed, and wonder why it
> > > displayed it that way. Whereas "(fault)" is quite obvious for any %p
> > > use case.
> >
> > I would immediately understand there's a missing IS_ERR() check in a
> > function that can return  -EINVAL, without having to add a new printk()
> > to find out what kind of bogus value has been received, and without
> > having to reboot, and trying to reproduce...
>
> I have to ask. Has there actually been a case that you used a %pX and
> it faulted, and you had to go back to find what the value of the
> failure was?

If it faulted, the bad pointer value is obvious from the backtrace.
If the code avoids the fault by verifying the pointer and returning
"(efault)" instead, the bad pointer value is lost.

Or am I missing something?

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds