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

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Date:	Thu, 14 Jul 2011 13:38:35 -0700
From:	Mike Waychison <mikew@...gle.com>
To:	"H. Peter Anvin" <hpa@...or.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 Thu, Jul 14, 2011 at 1:37 PM, H. Peter Anvin <hpa@...or.com> wrote:
> 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.

Are there existing examples of this already in the tree?
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