From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761018AbbKTUpG (ORCPT ); Fri, 20 Nov 2015 15:45:06 -0500 Received: from mail-ig0-f178.google.com ([209.85.213.178]:38161 "EHLO mail-ig0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760385AbbKTUpD (ORCPT ); Fri, 20 Nov 2015 15:45:03 -0500 MIME-Version: 1.0 In-Reply-To: References: <20151120173133.24259.97028.stgit@dwillia2-desk3.jf.intel.com> <20151120201207.GH8644@n2100.arm.linux.org.uk> Date: Fri, 20 Nov 2015 12:45:02 -0800 X-Google-Sender-Auth: bjh8LABz1jDMsAg72J7KxMnGY1I Message-ID: Subject: Re: [RFC PATCH] restrict /dev/mem to idle io memory ranges From: Kees Cook To: Dan Williams Cc: Russell King - ARM Linux , "linux-kernel@vger.kernel.org" , Greg Kroah-Hartman , Catalin Marinas , linux-nvdimm , Heiko Carstens , Will Deacon , Ingo Molnar , Benjamin Herrenschmidt , "H. Peter Anvin" , Martin Schwidefsky , Thomas Gleixner , Andrew Morton , "linux-arm-kernel@lists.infradead.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 On Fri, Nov 20, 2015 at 12:26 PM, Dan Williams wrote: > On Fri, Nov 20, 2015 at 12:12 PM, Russell King - ARM Linux > wrote: >> On Fri, Nov 20, 2015 at 09:31:33AM -0800, Dan Williams wrote: >>> This effectively promotes IORESOURCE_BUSY to IORESOURCE_EXCLUSIVE >>> semantics by default. If userspace really believes it is safe to access >>> the memory region it can also perform the extra step of disabling an >>> active driver. This protects device address ranges with read side >>> effects and otherwise directs userspace to use the driver. >> >> I'm happy with this as long as we retain the option to disable this >> new behaviour. >> >> The reason being, when developing a driver, it is _very_ useful to >> be able to poke around in the device's (and system memory) address >> spaces with tools like devmem2 to work out what's going on when >> things go wrong. >> >> To put it another way, I think it's a good idea to disable access to >> these regions on production systems, but for driver development, we >> want to retain the ability to poke around in physical address space >> in any way we so desire. >> > > Sounds ok to me, but I do think it's a good idea to default it to the > same value as STRICT_DEVMEM. Perhaps: > > bool "Filter I/O access to /dev/mem" if EXPERT > default STRICT_DEVMEM > > When this in do we even need IORESOURCE_EXCLUSIVE? It's barely used. Let's leave it for now to give us the debugging granularity Russell mentioned. If it turns out it's never used, we can drop it in the future. -Kees -- Kees Cook Chrome OS Security