[A83] Re: 83p os
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[A83] Re: 83p os
On Thu, 17 Apr 2003 14:31:34 +0200 (MEST)
robvanwijk@gmx.net wrote:
> > If you already change the jumps you can also check that no program
> > has an IM2 instruction in it. But when you have self modifying code
> > it's very difficult to check.
>
> It's even worse. IM 2 translates to ED5F, but a program can very well
> contain
> ED5F without switching to interrupt mode 2. For instance, 21ED5F is
> perfectly
> legal, as it means ld HL,$5FED. But checking the byte before ED5F does
> not guarantee anything either. Consider the following:
>
> DirtyTrick:
> ld HL,$5FED
> ... some code ...
> jp DirtyTrick+1
>
> The only "solution" that I can think of is telling programmers they're
> not allowed
> to use IM 2, and trust they'll comply.
>
> Rob van Wijk
>
> --
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>
>
This OS isn't a secure OS, it is made to multitask. You can take over
the entire calc from a app in ti-os, even if ti doesn't support it.
--
Max Sikstrom
pengi@molik.org
MoLiK programming and demo group
http://www.molik.org/
References: