Re: [PATCH-v2] iopl.2: Updating description of permissions and disabling interrupts

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

Hello Thomas,

On 6/26/20 10:29 PM, Thomas Piekarski wrote:
> Updating description of permissions for port-mapped I/O set per-thread 
> and not per-process. Mentioning iopl can not disable interrupts since 
> 5.5 anymore and is in general deprecated and only provided for legacy X 
> servers.
> 
> See https://bugzilla.kernel.org/show_bug.cgi?id=205317
> 
> Reported-by: victorm007@yahoo.com
> Signed-off-by: Thomas Piekarski <t.piekarski@deloquencia.de>

Thanks! I've applied this patch.

Cheers,

Michael

> ---
>   man2/iopl.2 | 34 ++++++++++++++--------------------
>   1 file changed, 14 insertions(+), 20 deletions(-)
> 
> diff --git a/man2/iopl.2 b/man2/iopl.2
> index e5b216a14..be9acfd1e 100644
> --- a/man2/iopl.2
> +++ b/man2/iopl.2
> @@ -39,29 +39,17 @@ iopl \- change I/O privilege level
>   .BI "int iopl(int " level );
>   .SH DESCRIPTION
>   .BR iopl ()
> -changes the I/O privilege level of the calling process,
> +changes the I/O privilege level of the calling thread,
>   as specified by the two least significant bits in
>   .IR level .
>   .PP
> -This call is necessary to allow 8514-compatible X servers to run under
> -Linux.
> -Since these X servers require access to all 65536 I/O ports, the
> -.BR ioperm (2)
> -call is not sufficient.
> +The I/O privilege level for a normal thread is 0.
> +Permissions are inherited from parents to children.
>   .PP
> -In addition to granting unrestricted I/O port access, running at a higher
> -I/O privilege level also allows the process to disable interrupts.
> -This will probably crash the system, and is not recommended.
> -.PP
> -Permissions are not inherited by the child process created by
> -.BR fork (2)
> -and are not preserved across
> -.BR execve (2)
> -(but see NOTES).
> -.PP
> -The I/O privilege level for a normal process is 0.
> -.PP
> -This call is mostly for the i386 architecture.
> +This call is deprecated, significantly slower than
> +.BR ioperm(2)
> +and is only provided for older X servers which require
> +access to all 65536 I/O ports. It is mostly for the i386 architecture.
>   On many other architectures it does not exist or will always
>   return an error.
>   .SH RETURN VALUE
> @@ -79,7 +67,7 @@ is greater than 3.
>   This call is unimplemented.
>   .TP
>   .B EPERM
> -The calling process has insufficient privilege to call
> +The calling thread has insufficient privilege to call
>   .BR iopl ();
>   the
>   .B CAP_SYS_RAWIO
> @@ -99,6 +87,12 @@ and in
>   .IR <sys/perm.h> .
>   Avoid the latter, it is available on i386 only.
>   .PP
> +Prior to Linux 5.5
> +.BR iopl ()
> +allowed the thread to disable interrupts while running
> +at a higher I/O privilege level. This will probably crash
> +the system, and is not recommended.
> +.PP
>   Prior to Linux 3.7,
>   on some architectures (such as i386), permissions
>   .I were
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/