Re: [Syllable-kernel] IO operations

[Daniel G. <da...@fp...>]

On Tue, 2004-12-14 at 19:52 +0100, Jacek wrote:
> Daniel wrote:
> > On Tue, 2004-12-14 at 18:21 +0100, Jacek wrote:
> >> 1. all kernel and application code currently runs on privilege level 0
> >
> >Nope.  User code runs at level 3.
> 
> That's great for me, half of work is done.
> 
> > I believe iopl is allowed (optionally) to root.  Anything not run as
> > root does not have iopl access.
> 
> Unfortunately you're not right. You can make a simple test:
> 
> // this will disable your PS/2 mouse
> int main() {
>         asm("mov $0xA7, %al;out %al, $0x64");
> }
> 
> sending 0xA8 to the same port will enable your mouse back
> 
> And the following code will reset your computer immediately (run it at your 
> own risk)
> int main() {
>         asm("mov $0xFE, %al;out %al, $0x64");
> }
> 
> What about other questions?

Yes, but unless you made a new account to log in as, you are running as
root, and therefore have iopl.

The Appserver, being started by init (which runs as root) will always
have iopl permission.

I didn't see any other questions in the original email?

Daniel