Message from Dejanews about this new bug. Using this bug, *any* user
   who
   can execute code on a Pentium box under *any* OS under *any* privelege
   level can crash the Pentium.
   
   -- cut here --
   Maybe, bugs like this will make Intel chips lose momemtum in the
   mission-critical enterprise-wide applications. You heard it here
   first.
   
   unsigned char x [5] = { 0xf0, 0x0f, 0xc7, 0xc8 };
   main ()
   {
   void (*f)() = (void (*)()) x;
   }
   
   This program should cause the OS to complain about an invalid
   instruction.
   But it doesn't. Aparently what it does is gives the CPU a very special
   invalid instruction, causing the CPU to come to a screeching halt. I'm
   told that it works on any Pentium running any OS. It does not need the
   CPU to be in privileged mode; it can be run in user space on operating
   systems that know the difference.
   
   I can confirm it halts two Pentium systems under Linux. I've heard it,
   uh,
   runs under NT and 95.
   
   This is not a serious problem for single user machines where crashing
   is only
   punishing one user, but could be nasty on multi-user machines.
   
   It looks like an invalid form of LOCK CMPXCHG8B.
   
   F0 0F C7 = LOCK CMPXCHG8B and C8 means 'register addressing with AX'
   (which makes no sense).
   
   -- cut here --
   
   You can try looking at http://www.x86.org/. That is an excellent site
   for
   undocumented stuff about Intel chips. There is an interesting incident
   involving how Intel harassed him.