linux-kernel - Re: [PATCH 2/2] x86: Allow disabling of sys_iopl, sys

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Message-ID: <4E1F5380.9020709@zytor.com>
Date:	Thu, 14 Jul 2011 13:37:20 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mike Waychison <mikew@...gle.com>
CC:	Greg Kroah-Hartman <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86: Allow disabling of sys_iopl, sys_ioperm

On 07/14/2011 01:34 PM, Mike Waychison wrote:
> In some build environments, it is useful to allow disabling of IO
> accesses to hardware, without having to rely on CAP_SYS_RAWIO (which is
> already overloaded to mean many other things).  One way that userland
> has access to IO accesses is via the iopl(2) and ioperm(2) system calls.
> 
> Allow disabling of these system calls from ever being available via a
> configuration option, X86_SYS_IOPL.   This is implemented by simply
> stubbing out the system calls and having them return ENOSYS when their
> functionality is disabled.
> 
> Note that we default this option to 'y', so that existing kernel configs
> will continue to support sys_iopl and sys_ioperm as before.
> 

Wouldn't it be more useful for this to be a sysctl?  In particular, like
many similar things it probably should be a lockable sysctl (three
states: enabled, disabled, and locked-disabled).

Making it a compile-time option I'm very skeptical to.

	-hpa
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