linux-kernel - Re: [PATCH]: linux-2.6.21-uc0 (MMU-less updates)

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Message-ID: <4639C164.5070908@snapgear.com>
Date:	Thu, 03 May 2007 21:03:00 +1000
From:	Greg Ungerer <gerg@...pgear.com>
To:	Robin Getz <rgetz@...ckfin.uclinux.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH]: linux-2.6.21-uc0 (MMU-less updates)

Robin Getz wrote:
> On Wed 2 May 2007 07:32, Greg Ungerer pondered:
>> Robin Getz wrote:
>>> On Wed 2 May 2007 01:23, Greg Ungerer pondered:
>>>> diff -Naur linux-2.6.21/fs/namei.c linux-2.6.21-uc0/fs/namei.c
>>>> --- linux-2.6.21/fs/namei.c     2007-05-01 17:12:53.000000000 +1000
>>>> +++ linux-2.6.21-uc0/fs/namei.c 2007-05-01 17:16:18.000000000 +1000
>>>> @@ -120,12 +120,14 @@
>>>>         int retval;
>>>>         unsigned long len = PATH_MAX;
>>>>
>>>> +#ifdef CONFIG_MMU
>>>>         if (!segment_eq(get_fs(), KERNEL_DS)) {
>>>>                 if ((unsigned long) filename >= TASK_SIZE)
>>>>                         return -EFAULT;
>>>>                 if (TASK_SIZE - (unsigned long) filename < PATH_MAX)
>>>>                         len = TASK_SIZE - (unsigned long) filename;
>>>>         }
>>>> +#endif
>>>>
>>>>         retval = strncpy_from_user(page, filename, len);
>>>>         if (retval > 0) {
>>> I was trying to understand why we don't want to do the same checking on
>>> noMMU?
>> The problem is on systems that have RAM mapped at high physical
>> addresses. TASK_SIZE may well be a numerically smaller number
>> than the address range that RAM sits in. So this test fails when
>> it shouldn't.
> 
> So, then this is a problem only on one or two architectures, not all noMMU 
> platforms?

Its not an architecture problem. It can effect any board that
has RAM mapped at a large numerical addresses (larger than TASK_SIZE).
So it can effect any non-MMU platform.

Regards
Greg



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