8086 memory space was: The Soul of Barb's New Machine 1158

And "executeable" file may consist of one or more of the following "block" types:

Executeable - being pure machine instructions which may only be referenced by the program counter in user mode (i.e. when the program is running its own code.)

Readonly - being immutable data that may be read but will fault when the processor tries to set the program counter to it or the processor attempts to write. Such would also apply to "shell scripts" and other interpreted programs handled by the "kernel".

Read-Write Data - data space that produces a fault if the program counter points into it.

Those are memory protection modes; not file modes. It requires only two bits per page-segment.

In the typical Unix process model for example, the appropriate modes would be initially set by the exec*() system calls, with VM doing its business as determined at exec time.

If you want to avoid the possibility of buffer overflow exploits, etc, then you have to pay for it by eliminating the possibility of self-modifying code. A small price to pay.

You can still feed the programs garbage... and the programs can generate all the garbage that they want (or don't; as may be the case); but they won't be able to physically execute garbage without the cooperation of the operating system to execute another program.

Garbage? Garbage instructions? Garbage *data* input isn't prevented by any of the above-described measures. What the measures prevent is that garbage being executed as processor instructions.

The compiler does it. Using BSS, etc.

None of that is necessary with proper memory management.

The only thing it stops you from doing is directly bashing a live operating system. A real operating system doesn't NEED such funny business any more... :-) you'd instead craft the patch (TEST!) and invoke a privileged system call to do the business; vectoring to the replacement routines before it unmaps the obsoleted. -- "Bernd Felsche - Innovative Reckoning, Perth, Western Australia ASCII ribbon campaign I'm a .signature virus! X against HTML mail Copy me into your ~-.signature and postings to help me spread!