Re: Partial Hardware Protection for Buffer Overrun Exploits

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Frank J. Lhota" <NOSPAM.FrankLho@rcn.com> writes:

> The first Intel chips that supported protected mode were the rarely-used
> 80186

The 80186 did not support protected mode.  It was practically identical
in architecture to an 8086 or 8088.  The 80186 had a small number of
additional instructions -- e.g., pushall for pushing all registers, I
think (for some definition of "all").

It was used in mainly in embedded systems, I believe.

>... and the 80286 chips that powered the IBM PC/AT. These early chips
> supported a command for transitioning from real to protected mode, but no
> simple command for transitioning back to real mode. This is what earned
> these chips the "brain dead" assessment from Gates. 

Well it *was* pretty brain dead, for this and other reasons.

>...The lack of a quick way
> to get back to real mode was a problem for MS, who wanted protected-mode
> extensions to DOS (such as Windows 3.x and OS/2 1.x) to be able to use the
> real mode I/O kernel of DOS. Their solution was the "mini-reboot" of the
> CPU, for which they paid a performance penalty.
> 
> All of these problems went away with the next generation of Intel chips (the
> 80386 and beyond), which can quickly toggle between real and protected
> modes.

Right.  In fact, the 80386 introduced "virtual 8086 mode", which allows
multiple real-mode virtual 8086 machines running on the same machine.

- Bob