linux-kernel - RE: [PATCH 05/12] unicore32 additional architecture files: low-level lib: uaccess

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Date:	Mon, 28 Feb 2011 09:04:42 +0800
From:	"Guan Xuetao" <gxt@...c.pku.edu.cn>
To:	"'Arnd Bergmann'" <arnd@...db.de>
Cc:	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
	"'Greg KH'" <greg@...ah.com>
Subject: RE: [PATCH 05/12] unicore32 additional architecture files: low-level lib: uaccess



> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@...db.de]
> Sent: Monday, February 28, 2011 1:22 AM
> To: Guan Xuetao
> Cc: linux-kernel@...r.kernel.org; linux-arch@...r.kernel.org; 'Greg KH'
> Subject: Re: [PATCH 05/12] unicore32 additional architecture files: low-level lib: uaccess
> 
> On Sunday 27 February 2011, Guan Xuetao wrote:
> > > -----Original Message-----
> > > From: Arnd Bergmann [mailto:arnd@...db.de]
> > > Sent: Friday, February 18, 2011 1:45 AM
> > > To: Guan Xuetao
> > > Cc: linux-kernel@...r.kernel.org; linux-arch@...r.kernel.org; 'Greg KH'
> > > Subject: Re: [PATCH 05/12] unicore32 additional architecture files: low-level lib: uaccess
> > >
> > > On Wednesday 16 February 2011, Guan Xuetao wrote:
> > > > +
> > > > +#define __kernel_ok                (segment_eq(get_fs(), KERNEL_DS))
> > > > +#define __user_ok(addr, size)      (((size) <= TASK_SIZE)                  \
> > > > +                           && ((addr) <= TASK_SIZE - (size)))
> > > > +#define __access_ok(addr, size)    (__kernel_ok || __user_ok((addr), (size)))
> > >
> > > A nice trick to simplify this is to introduce a per-process variable for comparing
> > > the pointer, set_fs() then sets this variable to either TASK_SIZE or
> > > UINT_MAX.
> >
> > Perhaps like this:
> > 1. add a member named kaddr in thread_info
> > 2. add following assignment codes in set_fs:
> >         current_thread_info()->kaddr =  segment_eq(fs, KERNEL_DS) ? UINT_MAX : TASK_SIZE;
> > 3. then __access_ok will be:
> >         #define addr
> >         #define __access_ok(addr, size)   (((size) <= TASK_SIZE)                        \
> >                                 && ((addr) <= current_thread_info()->kaddr)  - (size)))
> 
> That would also work. What I meant was to have
> 
> #define set_fs(fs) \
> 	do { current_thread_info()->kaddr = (fs); } while (0)
> 
> #define KERNEL_DS	UINT_MAX
> #define USER_DS		TASK_SIZE
> 
> Either way is fine with me, just choose whichever works best for you in terms of code size.
I can't find the difference between this way and the way in asm-generic/uaccess.h.
Perhaps, under this idea, __kernel_ok could be ignored.

> 
> 	Arnd

Thanks & Regards.
Guan Xuetao

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