Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754073AbbEKVXc (ORCPT ); Mon, 11 May 2015 17:23:32 -0400 Received: from mail-wg0-f49.google.com ([74.125.82.49]:36162 "EHLO mail-wg0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751564AbbEKVXa (ORCPT ); Mon, 11 May 2015 17:23:30 -0400 MIME-Version: 1.0 In-Reply-To: <20150511221125.177336d6@lxorguk.ukuu.org.uk> References: <20150511221125.177336d6@lxorguk.ukuu.org.uk> From: Alex Henrie Date: Mon, 11 May 2015 15:23:08 -0600 Message-ID: Subject: Re: ioperm is preserved across fork and execve, but iopl is not To: One Thousand Gnomes Cc: Kees Cook , "H. Peter Anvin" , Doug Johnson , Thomas Gleixner , Ingo Molnar , Tyler Hicks , Al Viro , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1577 Lines: 34 2015-05-11 15:11 GMT-06:00 One Thousand Gnomes : > Is there a real world use case ? Back in 2012 I needed to make a legacy program run that accessed the parallel port directly. Rewriting the program was not an option. So I wrote a helper program that used iopl and execve to grant the necessary permissions, but it only worked on 32-bit kernels. Then I realized that I could do the same thing with ioperm, and my problem went away, but the difference in behavior between iopl and ioperm has bothered me ever since. 2015-05-11 14:56 GMT-06:00 H. Peter Anvin : > 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(). I thought the general philosophy is that a privileged process can do anything it wants to. Removing the ability to disable interrupts in user space, or removing the ability to use iopl across execve, seems contrary to that goal. Still, if there is a security concern resulting from preserving iopl across execve, maybe the best thing to do is leave iopl and ioperm exactly as they are, update the documentation, and tell people to use ioperm whenever possible. -Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/