Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932480AbdCITSt (ORCPT ); Thu, 9 Mar 2017 14:18:49 -0500 Received: from mail-it0-f53.google.com ([209.85.214.53]:37159 "EHLO mail-it0-f53.google.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752441AbdCITSr (ORCPT ); Thu, 9 Mar 2017 14:18:47 -0500 MIME-Version: 1.0 In-Reply-To: <1489080561-30786-1-git-send-email-tycho@docker.com> References: <1489080561-30786-1-git-send-email-tycho@docker.com> From: Kees Cook Date: Thu, 9 Mar 2017 11:18:17 -0800 X-Google-Sender-Auth: 9vCFQwpOrBv1WQdEOgPYyAXOc3I Message-ID: Subject: Re: [PATCH] security/Kconfig: further restrict HARDENED_USERCOPY To: Tycho Andersen Cc: James Morris , linux-security-module , LKML , "Serge E. Hallyn" 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: 1888 Lines: 60 On Thu, Mar 9, 2017 at 9:29 AM, Tycho Andersen wrote: > It doesn't make sense to have HARDENED_USERCOPY when either /dev/kmem is > enabled or /dev/mem can be used to read kernel memory. > > v2: add !MMU depend as well Sorry I keep revising my thoughts on this... so, the bad combos, IMO, are /dev/kmem or /dev/mem. kmem is easy: we unconditionally require !DEVKMEM. The /dev/mem one continues to hurt my head, but here's my current thinking (which, if it seems correct should likely be reflected in the commit message): The following cases for /dev/mem should be safe: - /dev/mem entirely disabled (!DEVMEM) - /dev/mem with strict checking (STRICT_DEVMEM) Everything else is not okay, i.e. if an architecture lacks ARCH_HAS_DEVMEM_IS_ALLOWED, we must reject DEVMEM entirely since it cannot select STRICT_DEVMEM. So, sorry for the confusion, but I think this is the correct combo: depends on !DEVKMEM depends on !DEVMEM || STRICT_DEVMEM That should cover it, unless I'm still thinking sideways. -Kees > > Signed-off-by: Tycho Andersen > CC: Kees Cook > CC: "Serge E. Hallyn" > CC: James Morris > --- > security/Kconfig | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/security/Kconfig b/security/Kconfig > index 3ff1bf9..aeabd40 100644 > --- a/security/Kconfig > +++ b/security/Kconfig > @@ -142,6 +142,8 @@ config HARDENED_USERCOPY > bool "Harden memory copies between kernel and userspace" > depends on HAVE_ARCH_HARDENED_USERCOPY > depends on HAVE_HARDENED_USERCOPY_ALLOCATOR > + depends on !DEVKMEM > + depends on !ARCH_HAS_DEVMEM_IS_ALLOWED || STRICT_DEVMEM || !MMU > select BUG > help > This option checks for obviously wrong memory regions when > -- > 2.7.4 > -- Kees Cook Pixel Security