From: Heiko Carstens <heiko.carstens@de.ibm.com>
To: Andreas Schwab <schwab@linux-m68k.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Andrew Morton <akpm@linux-foundation.org>,
Tuxist <tuxist@tuxist.de>,
Patrick McCarthy <patrickjmc@gmail.com>,
Finn Thain <fthain@telegraphics.com.au>,
Rusty Russell <rusty@rustcorp.com.au>,
Thomas Gleixner <tglx@linutronix.de>,
Darren Hart <dvhart@linux.intel.com>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Linux-Next <linux-next@vger.kernel.org>
Subject: Re: [BUG -next] "futex: switch to USER_DS for futex test" breaks s390
Date: Fri, 3 Jan 2014 17:09:24 +0100 [thread overview]
Message-ID: <20140103160924.GC4219@osiris> (raw)
In-Reply-To: <87ppo95azt.fsf@igel.home>
On Fri, Jan 03, 2014 at 04:41:10PM +0100, Andreas Schwab wrote:
> Heiko Carstens <heiko.carstens@de.ibm.com> writes:
>
> > There is also other code that relies on this: e.g. copy_mount_options() my be
> > called with KERNEL_DS.
>
> With KERNEL_DS you can *only* access kernel memory, which is unpagable.
> If you want to access user memory, you _must_ use USER_DS.
I didn't say anything else. copy_mount_options() will be called with KERNEL_DS
from e.g. do_mount_root().
> > If DEBUG_PAGEALLOC is turned on, it would crash badly in kernel space
> > if it crosses page boundaries and touches an invalid page, even though
> > it should survive...
>
> Accessing an invalid page in kernel space is _always_ a bug.
Even though the current futex check relies on working exception handling
for this case.
If the patch I posted gets merged as well, it really doesn't matter for me.
Martin and I discussed this today and we will change the s390 code so that
it will also survive very early USER_DS accesses (without valid current->mm)
since we also discovered a couple of other oddities in our code.
But theses changes would be too complex for -stable, imho.
next prev parent reply other threads:[~2014-01-03 16:09 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-03 14:19 [BUG -next] "futex: switch to USER_DS for futex test" breaks s390 Heiko Carstens
2014-01-03 14:42 ` Geert Uytterhoeven
2014-01-03 15:36 ` Heiko Carstens
2014-01-03 15:41 ` Andreas Schwab
2014-01-03 16:09 ` Heiko Carstens [this message]
2014-01-07 8:47 ` Heiko Carstens
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