Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756328Ab2JCQNs (ORCPT ); Wed, 3 Oct 2012 12:13:48 -0400 Received: from mail-ie0-f174.google.com ([209.85.223.174]:40943 "EHLO mail-ie0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756291Ab2JCQNq (ORCPT ); Wed, 3 Oct 2012 12:13:46 -0400 MIME-Version: 1.0 In-Reply-To: References: <20121002234934.GA9194@www.outflux.net> Date: Wed, 3 Oct 2012 09:13:45 -0700 X-Google-Sender-Auth: DhcUXnIaA8LTVJNqrhufojaADmA Message-ID: Subject: Re: [PATCH] mm: use %pK for /proc/vmallocinfo From: Kees Cook To: David Rientjes Cc: linux-kernel@vger.kernel.org, Andrew Morton , Minchan Kim , Joe Perches , Kautuk Consul , linux-mm@kvack.org, Brad Spengler Content-Type: text/plain; charset=ISO-8859-1 X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1880 Lines: 46 On Tue, Oct 2, 2012 at 10:37 PM, David Rientjes wrote: > On Tue, 2 Oct 2012, Kees Cook wrote: > >> >> In the paranoid case of sysctl kernel.kptr_restrict=2, mask the kernel >> >> virtual addresses in /proc/vmallocinfo too. >> >> >> >> Reported-by: Brad Spengler >> >> Signed-off-by: Kees Cook >> > >> > /proc/vmallocinfo is S_IRUSR, not S_IRUGO, so exactly what are you trying >> > to protect? >> >> Trying to block the root user from seeing virtual memory addresses >> (mode 2 of kptr_restrict). >> >> Documentation/sysctl/kernel.txt: >> "This toggle indicates whether restrictions are placed on >> exposing kernel addresses via /proc and other interfaces. When >> kptr_restrict is set to (0), there are no restrictions. When >> kptr_restrict is set to (1), the default, kernel pointers >> printed using the %pK format specifier will be replaced with 0's >> unless the user has CAP_SYSLOG. When kptr_restrict is set to >> (2), kernel pointers printed using %pK will be replaced with 0's >> regardless of privileges." >> >> Even though it's S_IRUSR, it still needs %pK for the paranoid case. > > So root does echo 0 > /proc/sys/kernel/kptr_restrict first. Again: what > are you trying to protect? Only CAP_SYS_ADMIN can change the setting. This is, for example, for containers, or other situations where a uid 0 process lacking CAP_SYS_ADMIN cannot see virtual addresses. It's a very paranoid case, yes, but it's part of how this feature was designed. Think of it as supporting the recent uid 0 vs ring 0 boundary. :) -Kees -- Kees Cook Chrome OS Security -- 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/