Re: Partial Hardware Protection for Buffer Overrun Exploits

["Frank J. Lhota" <NOSPAM.FrankLho@rcn.com>]

<tmoran@acm.org> wrote in message news:qRVoa.554917$3D1.304762@sccrnsc01...
>   When Intel came out with Protected Mode Bill Gates declared it "brain
> dead" and they came up with the "solution" of doing a restart of the CPU
> to shake off the shackles of protection.

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