linux-kernel - Re: TASK

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Date:	Tue, 3 Jun 2014 17:19:56 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	Greg Ungerer <gerg@...inux.org>, Rabin Vincent <rabin@....in>,
	Will Deacon <will.deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-xtensa@...ux-xtensa.org" <linux-xtensa@...ux-xtensa.org>,
	linux-m32r@...linux-m32r.org, linux-c6x-dev@...ux-c6x.org,
	microblaze-uclinux@...e.uq.edu.au,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Linux MM <linux-mm@...ck.org>,
	linux-m68k <linux-m68k@...ts.linux-m68k.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	"uclinux-dist-devel@...ckfin.uclinux.org" 
	<uclinux-dist-devel@...ckfin.uclinux.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	panchaxari <panchaxari.prasannamurthy@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: TASK_SIZE for !MMU

On Tue, Jun 3, 2014 at 4:11 PM, Uwe Kleine-König
<u.kleine-koenig@...gutronix.de> wrote:
>> I did that same change for m68k in commit cc24c40 ("m68knommu: remove
>> size limit on non-MMU TASK_SIZE"). For similar reasons as you need to
>> now.
> ok.
>
>> >>Thoughts?
>> >The problem is that current linus/master (and also next) doesn't boot on
>> >my ARM-nommu machine because the user string functions (strnlen_user,
>> >strncpy_from_user et al.) refuse to work on strings above TASK_SIZE
>> >which in my case also includes the XIP kernel image.
>>
>> I seem to recall that we were not considering flash or anything else
>> other than RAM when defining that original TASK_SIZE (back many, many
>> years ago). Some of the address checks you list above made some sense
>> if you had everything in RAM (though only upper bounds are checked).
>> The thinking was some checking is better than none I suppose.
> What is the actual meaning of TASK_SIZE? The maximal value of a valid
> userspace address?

Yes

$ git show cc24c40
commit cc24c405949e3d4418a90014d10166679d78141a
Author: Greg Ungerer <gerg@...inux.org>
Date:   Mon May 24 11:22:05 2010 +1000

    m68knommu: remove size limit on non-MMU TASK_SIZE

    The TASK_SIZE define is used in some places as a limit on the size of
    the virtual address space of a process. On non-MMU systems those addresses
    used in comparison will be physical addresses, and they could be anywhere
    in the 32bit physical address space. So for !CONFIG_MMU systems set the
    TASK_SIZE to the maximum physical address.

    Signed-off-by: Greg Ungerer <gerg@...inux.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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