linux-kernel - Re: [RFC PATCH] arm: asm/cmpxchg.h: Add support half-word xchg()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150225171427.GE8656@n2100.arm.linux.org.uk>
Date:	Wed, 25 Feb 2015 17:14:27 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Pranith Kumar <bobby.prani@...il.com>,
	"moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] arm: asm/cmpxchg.h: Add support half-word xchg()

On Wed, Feb 25, 2015 at 05:21:54PM +0100, Arnd Bergmann wrote:
> On Wednesday 25 February 2015 11:11:28 Pranith Kumar wrote:
> > On Wed, Feb 25, 2015 at 10:58 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > > On Wednesday 25 February 2015 10:36:20 Pranith Kumar wrote:
> > >> This patch adds support for a half-word xchg() for ARM using ldrexh/strexh
> > >> instructions. It also fixes an asm comment  for __cmpxchg2.
> > >>
> > >> Currently using a half-word xchg() results in the following splat on an ARMv7
> > >> machine.
> > >>
> > >> [   45.833303] xchg: bad data size: pc 0xbe806020, ptr 0xeb18deee, size 2
> > >> [   45.833324] ------------[ cut here ]------------
> > >> [   45.837939] kernel BUG at /dvs/git/dirty/git-master_linux/kernel/arch/arm/kernel/traps.c:727!
> > >>
> > >> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
> > >
> > > Unfortunately, the BUG message seems incomplete, can you reproduce this
> > > with CONFIG_DEBUG_BUGVERBOSE enabled?
> > 
> > The bug here is in a module caused when xchg() was used on uint16_t
> > variable. It is caused by the __bad_xchg() for 2 byte swap.
> > 
> > More information:
> > [   45.833303] xchg: bad data size: pc 0xbe806020, ptr 0xeb18deee, size 2
> > [   45.833324] ------------[ cut here ]------------
> > [   45.837939] kernel BUG at
> > /dvs/git/dirty/git-master_linux/kernel/arch/arm/kernel/traps.c:727!
> > [   45.846450] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
> > [   45.852275] Modules linked in: test(O+) nvhost_vi
> > [   45.857012] CPU: 0 PID: 1848 Comm: insmod Tainted: G           O
> > 3.10.24-g6a2d13a #1
> > [   45.864744] task: ee406580 ti: eb18c000 task.ti: eb18c000
> > [   45.870141] PC is at __bad_xchg+0x24/0x28
> > [   45.874146] LR is at __bad_xchg+0x24/0x28
> 
> I'm more interested in the backtrace here, it's possible we should fix the
> driver instead.

Actually, I think we ought to get rid of __bad_xchg() so that cases
like this cause a link error instead of a runtime error, just like we
do in other cases as well.

That's something that goes back ages (it used to be called something
like invalidptr in 2.0 kernels...)

-- 
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/