linux-kernel - Re: [PATCH 2/2] printk/console: Enhance the check for consoles using init memory

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Date:   Thu, 27 Jul 2017 11:29:57 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Matt Redfearn <matt.redfearn@...tec.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        "Fabio M. Di Nitto" <fdinitto@...hat.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] printk/console: Enhance the check for consoles using
 init memory

On Wed 2017-07-26 22:08:04, Sergey Senozhatsky wrote:
> On (07/14/17 14:51), Petr Mladek wrote:
> > printk_late_init() is responsible for disabling boot consoles that
> > use init memory. It checks the address of struct console for this.
> > 
> > But this is not enough. For example, there are several early
> > consoles that have write() method in the init section and
> > struct console in the normal section. They are not disabled
> > and could cause fancy and hard to debug system states.
> > 
> > It is even more complicated by the macros EARLYCON_DECLARE() and
> > OF_EARLYCON_DECLARE() where various struct members are set at
> > runtime by the provided setup() function.
> > 
> > I have tried to reproduce this problem and forced the classic uart
> > early console to stay using keep_bootcon parameter. In particular
> > I used earlycon=uart,io,0x3f8 keep_bootcon console=ttyS0,115200.
> > The system did not boot:
> > 
> > [    1.570496] PM: Image not found (code -22)
> > [    1.570496] PM: Image not found (code -22)
> > [    1.571886] PM: Hibernation image not present or could not be loaded.
> > [    1.571886] PM: Hibernation image not present or could not be loaded.
> > [    1.576407] Freeing unused kernel memory: 2528K
> > [    1.577244] kernel tried to execute NX-protected page - exploit attempt? (uid: 0)
> > 
> > The double lines are caused by having both early uart console and
> > ttyS0 console enabled at the same time. The early console stopped
> > working when the init memory was freed. Fortunately, the invalid
> > call was caught by the NX-protexted page check and did not cause
> > any silent fancy problems.
> > 
> > This patch adds a check for many other addresses stored in
> > struct console. It omits setup() and match() that are used
> > only when the console is registered. Therefore they have
> > already been used at this point and there is no reason
> > to use them again.
> > 
> > Signed-off-by: Petr Mladek <pmladek@...e.com>
> 
> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>

Thanks for the review. I am going to push the two patches into
for-4.14 branch so that we could get some testing via linux-next.

Best Regards,
Petr