Port access

[hunter]

Hello,

is it possible to disable the ports and cli,sti,... for ring3 tasks ??
Could somebody give me a example ?

Hunter

[Jeko]

Hello,

is it possible to disable the ports and cli,sti,... for ring3 tasks ??
Could somebody give me a example ?

Hunter

I think you must use the TSS. cli and sti are already disabled in ring3.

[AJ]

Hi,

If you want to disable all ports in ring 3, simply set the IOPL bits in EFLAGS to zero. This means that any ring 3 task attempting port access will cause a GP fault. This needs to be appropriately handled by your kernel, which can decide whether or not to allow the read/write.

Cheers,
Adam

[hunter]

cli and sti are already disabled in ring3

But if i use cli in a ring3 task the system stops ... Should i have to do something to disable them ??

Hunter

[AJ]

No. If you are really running in ring 3, you will generate a GPF if you try to cli.

Also, you *cannot* modify IF with the POPF instruction if IOPL is set below the current privilege level.

Cheers,
Adam

[Combuster]

Once again: check IOPL

Also, some people forgot to read the manual page on CLI:

In protected mode and virtual-8086-mode, this instruction is IOPL-sensitive. If the CPL is less than or equal to the rFLAGS.IOPL field, the instruction clears IF to 0.

In protected mode, if IOPL < 3, CPL = 3, and protected mode virtual interrupts are enabled (CR4.PVI = 1), then the instruction instead clears rFLAGS.VIF to 0. If none of these conditions apply, the processor raises a general-purpose exception (#GP).