Privileged mode commands in FreeBSD processes

[Alfred Perlstein]

You can see i386_get_ldt(2) and io(4) manpages.

More privileged opcodes can not be used afaik.

* Victor <vicmrml at gmail.com> [110831 13:05] wrote:
> Is it possible to write and start a program in FreeBSD, which could 
> execute processor commands of previleged modes (protection rings), 
> commonly prohibited to a process in the user mode?
> 
> For example we could permit the process direct access to i/o ports (IN 
> and OUT commands on PC architecture), execution of the software 
> interrupt command with any operand (INT), access to descriptor tables 
> registers (GDT, LDT, etc.) with capability of changing content of both 
> these registers and descriptor tables themselves (situated in the RAM).  
> We could also allow the process to change flag bits in the registers of 
> CPU, responsible for processor modes (memory addressing modes, 
> transition from protected to real mode and vice versa, etc.) In fact, if 
> this feature exists in FreeBSD, it must switch the processor for the 
> time of execution this process to the mode with higher privileges (to 
> the protection ring from 2 to 0, not 3 in x86). I would like to ask the 
> FreeBSD community, does this possibility exist in FreeBSD?
> 
> I understand the problem can be easily solved by deviding the program 
> into two parts: the process (COFF or ELF file) and the driver. All the 
> code, containing privileged commands, could be placed in the driver, as 
> the rest of the code (its unprivileged part) could be contained in the 
> process. As far as I understand, the driver code is executed in the 0 
> ring mode, so it has no restrictions. On the other hand it would be 
> interesting to have such an opportunity for common processes in both 
> educational (e. g. studying assembler privileged mode commands) and 
> technical purposes. Of course this feature is a great threat for system 
> safety, and besides programs, using it, can easily completely destroy 
> the system, however it could be useful for some aims.
> 
> Does anything of such kind exist in FreeBSD? If it does, please give me 
> a reference in the FreeBSD documentation.
> 
> Victor.
> 
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-- 
- Alfred Perlstein
.- VMOA #5191, 03 vmax, 92 gs500, 85 ch250, 07 zx10
.- FreeBSD committer