linux-kernel - Re: [PATCH 1/3] arm/syscalls: Move address limit check in loop

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Message-ID: <20170725103828.GJ31807@n2100.armlinux.org.uk>
Date:   Tue, 25 Jul 2017 11:38:28 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Leonard Crestez <leonard.crestez@....com>
Cc:     Thomas Garnier <thgarnie@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Dave Martin <Dave.Martin@....com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Pratyush Anand <panand@...hat.com>,
        linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 1/3] arm/syscalls: Move address limit check in loop

On Tue, Jul 25, 2017 at 01:28:01PM +0300, Leonard Crestez wrote:
> On Mon, 2017-07-24 at 10:07 -0700, Thomas Garnier wrote:
> > On Wed, Jul 19, 2017 at 10:58 AM, Thomas Garnier <thgarnie@...gle.com
> > > wrote:
> > > 
> > > The work pending loop can call set_fs after addr_limit_user_check
> > > removed the _TIF_FSCHECK flag. To prevent the infinite loop, move
> > > the addr_limit_user_check call at the beginning of the loop.
> > > 
> > > Fixes: 73ac5d6a2b6a ("arm/syscalls: Check address limit on user-
> > > mode return")
> > > Reported-by: Leonard Crestez <leonard.crestez@....com>
> > > Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
> 
> > Any comments on this patch set?
> 
> Tested-by: Leonard Crestez <leonard.crestez@....com>
> 
> This appears to fix the original issue of failing to boot from NFS when
> there are lots of alignment faults. But this is a very basic test
> relative to the reach of this change.
> 
> However the original patch has been in linux-next for a while and
> apparently nobody else noticed system calls randomly hanging on arm.
> 
> I assume maintainers need to give their opinion.

I've already stated my opinion, which is different from what Linus has
requested of Thomas.  IMHO, the current approach is going to keep on
causing problems along the lines that I've already pointed out.

-- 
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