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To: linux-kernel@vger.kernel.org
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: ioperm() / iopl() irritation
Date: 28 Feb 2002 15:53:27 -0800
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Followup to:  <Pine.LNX.4.33.0202282128170.25655-100000@biker.pdb.fsc.net>
By author:    Martin Wilck <Martin.Wilck@fujitsu-siemens.com>
In newsgroup: linux.dev.kernel
>
> A short question that may be dumb:
> 
> In the docs on i386 IO protection that I know, it is said that
> the processor ANDs the two protection mechanisms offered by the
> IOPL flag and the io permission bitmap. That is, if IO permissions
> are granted through iopl(), but ports are masked in the IO permission
> bitmap, a segmentation fault should arise.
> 

Wrong.

> Such a situation should be generated by code like this:
> 
>   iopl(3);
>   ioperm (0,0x1f,1); /* 0x20-0x3ff remain masked */
>   c = inb (0x20);
> 
> However on my machine this codse is successful! How is that possible?

Because you have misunderstood how IOPL works.

	-hpa
-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt	<amsp@zytor.com>
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