linux-kernel - Re: [PATCH] init: use KERNEL_DS when trying to start init process

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Message-ID: <4DEFD979.50405@tilera.com>
Date:	Wed, 8 Jun 2011 16:20:09 -0400
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Mathias Krause <minipli@...glemail.com>
CC:	Al Viro <viro@...iv.linux.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>, <stable@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"David S. Miller" <davem@...emloft.net>,
	Chris Zankel <chris@...kel.net>
Subject: Re: [PATCH] init: use KERNEL_DS when trying to start init process

On 6/8/2011 8:14 AM, Mathias Krause wrote:
> On Wed, Jun 8, 2011 at 12:47 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
>> On Tue, Jun 07, 2011 at 07:00:24PM -0700, Linus Torvalds wrote:
>>> That said, that commit (it's commit ID 4095b99c09e3d in tglx's tree)
>>> predates the "real" BK history too: it's part of the (limited) 2.4.x
>>> history that was imported from the release patches into BK at the
>>> beginning of the use of BK. So at that point we didn't do indivual
>>> commits, it's just the import of the v2.4.3.7 -> v2.4.3.8 patch.
>>>
>>> But yeah, it's old and crufty. And I agree that usually the correct
>>> fix is to remove the set_fs() calls entirely.
>> I think these days its job is done by start_thread(), which is where we
>> switch to USER_DS; it's called by ->load_binary() when it decides it's past
>> the point of no return.  However, it would be a good idea to verify that
>> all architectures do it there properly and we are not exposing a hole by
>> removal of this set_fs()...
> I've checked all implementations of start_thread() and found some candidates:
>
> SPARC, TILE and Xtensa don't call set_fs(USER_DS), albeit have
> different definitions for USER_DS and KERNEL_DS. So those might need
> fixing. I'm not familiar with those architectures, so someone else has
> to answer this.

TILE relies on the set_fs() in search_binary_handler(), but adding
set_fs(USER_DS) in in start_thread() should be a valid change if the
set_fs() is removed from search_binary_handler().  I'm happy to ack the
obvious change for tile, or I can put the change to tile's start_thread()
in my tree for inclusion in 3.1, either way.

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com


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