From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f51.google.com (mail-wg0-f51.google.com [74.125.82.51]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 82C111A0315 for ; Wed, 5 Nov 2014 06:59:21 +1100 (AEDT) Received: by mail-wg0-f51.google.com with SMTP id l18so14276045wgh.38 for ; Tue, 04 Nov 2014 11:59:18 -0800 (PST) Date: Tue, 4 Nov 2014 19:59:14 +0000 From: Leif Lindholm To: Kees Cook Subject: Re: [RFC PATCH] make CONFIG_STRICT_DEVMEM a core non-debug feature Message-ID: <20141104195914.GY22224@bivouac.eciton.net> References: <1415121836-16241-1-git-send-email-leif.lindholm@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Cc: Catalin Marinas , Will Deacon , Oleg Nesterov , paulus@samba.org, "H. Peter Anvin" , Guan Xuetao , linux-s390@vger.kernel.org, Russell King - ARM Linux , "x86@kernel.org" , Christoph Hellwig , Ingo Molnar , dave.long@linaro.org, eiko.carstens@de.ibm.com, Arnd Bergmann , cmetcalf@tilera.com, Thomas Gleixner , Arjan van de Ven , "linux-arm-kernel@lists.infradead.org" , Greg KH , LKML , Andy Lutomirski , Martin Schwidefsky , linux390@de.ibm.com, Andrew Morton , linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Nov 04, 2014 at 10:43:00AM -0800, Kees Cook wrote: > > diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig > > index efefd12..39f7817 100644 > > --- a/drivers/char/Kconfig > > +++ b/drivers/char/Kconfig > > @@ -6,6 +6,22 @@ menu "Character devices" > > > > source "drivers/tty/Kconfig" > > > > +config STRICT_DEVMEM > > + bool "Reduced access to /dev/mem" > > + depends on HAVE_ARCH_RESTRICTED_DEVMEM > > + default y > > + help > > + If this option is disabled, you allow userspace (root) access to all > > + of memory, including kernel and userspace memory. Accidental > > + access to this is obviously disastrous, but specific access can > > + be used by people debugging the kernel. > > + > > + If this option is switched on, the /dev/mem file restricts userspace > > + access to an architecture-specific subset of the physical address > > + space. > > Great consolidation, thanks! I would probably expand this help text a > bit to include some of details mentioned in the x86 portion of the > option. For example: > > > If this option is switched on, the /dev/mem file restricts userspace > access to an architecture-specific subset of the physical address > space. For example on x86, PCI space and BIOS code and data > regions. This is sufficient for things like dosemu and non-KMS > Xorg and all common users of /dev/mem. I considered doing that, but didn't want to risk listing too many details of one architecture, and too few of others. One alternative would be to add a devmem.txt somewhere in Documentation, listing the behaviours on different architectures (this would also be a good place to describe restrictions on types of mappings and suchlike). The help message could then contain a mention of that file. Would that work for you? I really don't have a strong opinion however, and would be happy to go along with whatever the most people would like to see. / Leif