linux-kernel - Re: Fwd: ioperm is preserved across fork and execve, but iopl is not

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Message-ID: <55511782.30303@zytor.com>
Date:	Mon, 11 May 2015 13:56:34 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Alex Henrie <alexhenrie24@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Doug Johnson <dougvj@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Tyler Hicks <tyhicks@...onical.com>,
	Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: Fwd: ioperm is preserved across fork and execve, but iopl is
 not

On 05/11/2015 01:49 PM, Alex Henrie wrote:
> 
> The ioperm and iopl calls are both used to grant a process permission
> to access I/O devices directly. iopl(3) is equivalent to ioperm(0,
> 0xFFFF, 1). However, permissions granted through ioperm are preserved
> across fork and execve, and permissions granted through iopl are not.
> This makes no sense: The two calls do the same thing, so there is no
> security benefit to dropping one on fork or execve but not the other.
> 

They don't, in fact.  An iopl(3) process is allowed to disable
interrupts in user space, which an ioperm() process is not.

This is a HUGE deal.  This really makes me wonder if iopl(3) should be
allowed at all, or if we should just intercept it and treat it as ioperm().
	
	-hpa


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