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

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Message-ID: <20190510144917.lrgftg4wjfcyxoku@pathway.suse.cz>
Date:   Fri, 10 May 2019 16:49:17 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Tobin C . Harding" <me@...in.cc>, Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, Russell Currey <ruscur@...sell.cc>,
        Christophe Leroy <christophe.leroy@....fr>,
        Stephen Rothwell <sfr@...abs.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        linux-arch@...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 Fri 2019-05-10 10:42:13, Petr Mladek wrote:
> The commit 3e5903eb9cff70730 ("vsprintf: Prevent crash when dereferencing
> invalid pointers") broke boot on several architectures. The common
> pattern is that probe_kernel_read() is not working during early
> boot because userspace access framework is not ready.
> 
> It is a generic problem. We have to avoid any complex external
> functions in vsprintf() code, especially in the common path.
> They might break printk() easily and are hard to debug.
> 
> Replace probe_kernel_read() with some simple checks for obvious
> problems.

JFYI, I have sent a pull request with this patch, see
https://lkml.kernel.org/r/20190510144718.riyy72g4cy5nkggx@pathway.suse.cz

Best Regards,
Petr