linux-kernel - Re: [PATCH 1/2] char/mem: Add /dev/io (v2)

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Message-ID: <4F31C417.30502@redhat.com>
Date:	Tue, 07 Feb 2012 19:38:47 -0500
From:	Adam Jackson <ajax@...hat.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	linux-kernel@...r.kernel.org, arnd@...db.de,
	gregkh@...uxfoundation.org
Subject: Re: [PATCH 1/2] char/mem: Add /dev/io (v2)

On 2/7/12 7:17 PM, Alan Cox wrote:
> On Tue,  7 Feb 2012 18:39:45 -0500
> Adam Jackson<ajax@...hat.com>  wrote:
>
>> This is like /dev/port except not broken.  /dev/port will translate all
>> read/write into inb/outb streams, which is wrong since hardware can and
>> does care about cycle size.  /dev/io will only allow 1, 2, or 4 byte
>> access, and will translate that into the appropriate bus cycle size.
>
> From a security perspective /dev/[k][mem is a dumb bit of ancient Unix
> history we'd dearly like to kill off. /dev/port is a similar early PC
> unixism that wants to go the same way. /dev/io just adds another horror
> to the pile.
>
> Please do the decent thing, stop using /dev/mem and /dev/port for
> anything. If you need to access an I/O device make it properly visible
> via the kernel only for the ports and in a manner that is safe.

Yeah, I'll be sure to do that right as soon as I can stop supporting the 
vesa driver.  Until that time I don't really have any choice but to 
expose the whole of I/O port space, since I have no idea what the video 
BIOS is going to touch.

I don't disagree with wanting to limit access to these services, but 
/dev/io is at least somewhat containable, whereas iopl is insane.

- ajax

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