Date: Sat, 10 May 2003 23:50:07 -0400
From: Chuck Ebbert <76306.1226@compuserve.com>
Subject: Re: desc v0.61 found a 2.5 kernel bug
To: Gabriel Paubert <paubert@iram.es>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Message-ID: <200305102353_MC3-1-385A-BC35@compuserve.com>
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Gabriel Paubert wrote:

> The devil is in the details: you have to edit the TSS, clear the busy bit
> of the previous TSS, LTR, clear the busy bit of the debug TSS, restore
> many registers from the previous TSS image, switch to the kernel stack of
> the interrupted process, push a lot of stuff on the stack to be used by iret.
> (depending on whether you return to kernel/user/v86 modes). All of this in the 
> right order, of course (and after having cleared your own NT flag).

 And this is the way to do it right, but...

> Doable I believe but not simple, and there is still the TS issue.

 I finally realized the TS problem is basically unsolvable.  There is no
way to know what the value was before a switch happened.


 (BTW some other Free kernel has interesting things in its descriptor
tables: DPL 1 execute-only code segments, conforming code, expand-down
data, multiple LDTs etc...  It uncovered a bug in my code, too.)
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