snow

Hi guys!

Let say i have some random generated assembly code and i wonder if i can (and how) do this:
1) prevent this code of accessing memory except some part of it... let say restrict it to 1kb of memory
2) prevent jumps to outside of this code
3) prevent infinite loops... e.g. restrict execution of programme to max. number of cycles (or time) as accurate as possible

Any ideas, comments are welcome!

If i wasnt clear about something please ask!

DaWei

Build it into the OS.

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Polyphemus_

It's like dawei said... it has to be built into the OS. Only high-level, interpretted languages can prevent a program from doing such things.

snow

Hm.
What about timer interrupts for loops?

And if i could modify code a bit... with some algorithm.. so build in checking before every instruction that deals with memory or makes a jump?

DaWei

It has nothing to do with the language, or the level of it. It has to do with oversight of running code. This is accomplished with an executive that has control of the running of processes and the assignment and management of memory.

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Dameon

All 3 are part of the fundamental functioning of an OS for x86 protected mode. The ring-0 code can set up the pages or segments for running apps, which is why you can't overwrite memory in App B from App A without using system calls. Address X might map to address Y in physical memory for App A, but Address X might map to Address Z for App B. I forget if there's another way to do it, but I know that on some processors the kernel-mode code can set the NX bit on pages to, for example, prevent execution of code on the stack. And thanks to your timer interrupt, applications forcibly share time with the others at the discretion of the OS.

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DaWei

Your latter suggestion is somewhat akin to shoveling shit against the tide so as to make the sea shallower.

EDIT: Not Dameon's, that was a simultaneous post. Snows.

__________________
Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code.
Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers