From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C8F39C4727E for ; Fri, 25 Sep 2020 20:47:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 727B62086A for ; Fri, 25 Sep 2020 20:47:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="JbKkYCXQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728779AbgIYUrZ (ORCPT ); Fri, 25 Sep 2020 16:47:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56136 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726316AbgIYUrZ (ORCPT ); Fri, 25 Sep 2020 16:47:25 -0400 Received: from mail-pf1-x442.google.com (mail-pf1-x442.google.com [IPv6:2607:f8b0:4864:20::442]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 04D43C0613CE for ; Fri, 25 Sep 2020 13:47:25 -0700 (PDT) Received: by mail-pf1-x442.google.com with SMTP id n14so4369786pff.6 for ; Fri, 25 Sep 2020 13:47:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=7C9Zlz0e46DAdnF/e0XanUeFYdy+9ZLUi1QSq8iLKOY=; b=JbKkYCXQzwQllU+mY7rBbwtyc4aKP85Fzv8l0O0aNBSQ7X0rJgDlrdkAZjBdEleUZG L3Hu9ElKYQMmY+7PwpY3AUnhiBgNJpvZH0KNLZPnQIGHiI/xo9FQfoi8FCrI/4osGj9P 4Jo7IlLyZjYTLYtDH7ZYbeLb/IOF8laCZ1L34= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=7C9Zlz0e46DAdnF/e0XanUeFYdy+9ZLUi1QSq8iLKOY=; b=S66JRlNTGchjlCvb9VI8fGwzDS5rxk6Yjlyo2vjLZkVxX5hDgj2jZwayUNPuUoYpAX Eq8oFClaPxuhsnJAZ9r+HXlmaJ9+CLvVI6KwbCv7bsegJSbASRhTT8aX24A3KrYpnow4 nL5mVTroJDBW422DWcuR5NIdJc3/+8qyD4/SZOfBDttEaqw3g0SEgrzJ269NxrkCGniV pIru7s7BCv80A80PMHdyijFcRVdNDntd56/0YoEV3f15HcFq9Pk8Gv4lUidELg3VDFFl gwRc3jNeI0sTzV58sU7xVyS0dhniJlzo3n3y0d4WYBH9alY5TOUU+WiOxrEhdK1JuqAx oQoQ== X-Gm-Message-State: AOAM532C8ue6iRcPtLsRQ4hL/8WTCOkWUU7I+zgKa56V8iTmbtcvhml9 Ed0RJRhAjup4IVrUv+zTq4h+Kw== X-Google-Smtp-Source: ABdhPJwXuuaq9yCDdhG5xfeSQsX8WManjyq4C6vgn5JVdTwM5yDXqA9A3/qBkjtkvxVMDDk7ZLiRjA== X-Received: by 2002:a63:6bc9:: with SMTP id g192mr635581pgc.236.1601066844523; Fri, 25 Sep 2020 13:47:24 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id d5sm3599693pfq.72.2020.09.25.13.47.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Sep 2020 13:47:23 -0700 (PDT) Date: Fri, 25 Sep 2020 13:47:22 -0700 From: Kees Cook To: Ard Biesheuvel Cc: Pintu Agarwal , Mark Rutland , Arnd Bergmann , Ard Biesheuvel , Marc Zyngier , Dave Martin , Kernelnewbies , Russell King - ARM Linux , open list , Tony Lindgren , matt@codeblueprint.co.uk, nico@linaro.org, Thomas Garnier , "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" Subject: Re: KASLR support on ARM with Kernel 4.9 and 4.14 Message-ID: <202009251338.D17FB071@keescook> References: <202009251301.A1FD183582@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 25, 2020 at 10:37:01PM +0200, Ard Biesheuvel wrote: > On Fri, 25 Sep 2020 at 22:28, Kees Cook wrote: > > > > On Fri, Sep 25, 2020 at 08:33:59PM +0530, Pintu Agarwal wrote: > > > This is regarding the KASLR feature support on ARM for the kernel > > > version 4.9 and 4.14. > > > > > > Is KASLR supported on ARM-32 Linux 4.9 and above ? > > > > Sorry, this feature did not yet land in upstream: > > https://github.com/KSPP/linux/issues/3 > > > > Here was the earlier effort: > > https://lore.kernel.org/kernel-hardening/20170814125411.22604-1-ard.biesheuvel@linaro.org/ > > > > > Is it dependent on CONFIG_RANDOMIZE_BASE or > > > > CONFIG_RANDOMIZE_BASE is what is used on other architectures to control > > the feature. > > > > > /proc/sys/kernel/randomize_va_space ? > > > Is there any relation between these two? > > > > No, the latter is about userspace addresses. > > > > > Is the changing kernel symbols (in every boot), only possible if KASLR > > > is enabled, or there is another way it can happen? > > > > I think you meant kernel symbol addresses (not the symbols themselves). > > But yes, I wouldn't expect the addresses to move if you didn't either > > rebuild the kernel or had something else moving the kernel at boot (i.e. > > the boot loader). > > > > > I have these queries because, > > > In one of the arm-32 devices with Kernel 4.14, I observed that > > > CONFIG_RANDOMIZE_BASE is not available. > > > But /proc/sys/kernel/randomize_va_space is set to 2. > > > However, I also observed that symbol addresses are changing in every boot. > > > > > > 1st boot cycle: > > > [root ~]# cat /proc/kallsyms | grep "sys_open" > > > a5b4de92 T sys_open > > > [root@sa515m ~]# > > > > > > 2nd boot cycle: > > > [root ~]# cat /proc/kallsyms | grep "sys_open" > > > f546ed66 T sys_open > > > > > > So, I am wondering how this is possible without KASLR > > > (CONFIG_RANDOMIZE_BASE) support in Kernel ? > > Those addresses were obfuscated by kptr_restrict Is that true? kptr_restrict zeros (rather than hashing) the kallsyms view. And besides, the %p hashing was added in v4.15 (but also doesn't touch kallsyms, which does all-or-nothing to avoid breaking stuff like perf). -- Kees Cook