Fiasco.OC x86 IO port permission bitmap

Daniel Waddington d.waddington at
Tue Jan 24 22:12:03 CET 2012

Hi Adam,

I see. So it seems that you have to map all of the IO port space before 
getting IOPL raised to 3 (assuming Kconfig IO_PROT & !IO_PROT_3) and 
therefore the default mode of operation is a driver will map the whole 
space if it wants to use IO instructions directly.  Is it right that you 
currently don't use the TSS IO bitmap to allow access to only specific 
IO ports with CPL > IOPL?


On 01/24/2012 11:03 AM, Adam Lackorzynski wrote:
> Hi,
> On Mon Jan 23, 2012 at 15:54:29 -0800, Daniel Waddington wrote:
>> I want to use the TSS I/O permission bit map to support fine grained
>> control of I/O access for user-level apps (x86 32 bit target).  From
>> looking at the kernel code, I believe the bit map is switched out
>> per-process as part of the Context class (Space::_io_space) -
>> correct me if I am wrong.  My query is how to set/clear the bits for
>> a given target task from a "root" task with sufficient privileges
>> (e.g., base caps and sigma0 caps).  I could extend the kernel
>> scheduler protocol, but I don't want to do this if there is already
>> a clean way in place.
> IO-ports are handled similar to page-faults, i.e. they can be mapped to
> other tasks, and the pager receives io-page-faults when one of its
> clients accesses an IO-port without having it. For example look for
> L4_PROTO_IO_PAGE_FAULT and l4_iofpage().
> Adam
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