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=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 54E4CC4727C for ; Fri, 25 Sep 2020 23:49:37 +0000 (UTC) Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A17EF2086A for ; Fri, 25 Sep 2020 23:49:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="Vp5m6tCD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A17EF2086A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernelnewbies-bounces+kernelnewbies=archiver.kernel.org@kernelnewbies.org Received: from localhost ([::1] helo=shelob.surriel.com) by shelob.surriel.com with esmtp (Exim 4.94) (envelope-from ) id 1kLxT5-00087y-6n for kernelnewbies@archiver.kernel.org; Fri, 25 Sep 2020 19:49:35 -0400 Received: from mail-pg1-x542.google.com ([2607:f8b0:4864:20::542]) by shelob.surriel.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1kLxRN-0006gE-Oq for kernelnewbies@kernelnewbies.org; Fri, 25 Sep 2020 19:47:49 -0400 Received: by mail-pg1-x542.google.com with SMTP id e18so243932pgd.4 for ; Fri, 25 Sep 2020 16:47:48 -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=Io7hz4IuqZtEpaytzAzCxwSUam0CFx9DS3tqLdxn+Xk=; b=Vp5m6tCDtyV4W/JH0g4qWcc327nWVydhooFj9uwSpVAY0st4EEXpvloPDbNDLUzEge ywH/h1AoxE8vmj64+7NIXyeLfN4EvN1QEEZ1xgXXA/m9O9RMBN8i2YkTSTw3fwHOZvAq g0p+zzkkPf8d2ui3sxADVxcXOjMUhtNwsWnSk= 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=Io7hz4IuqZtEpaytzAzCxwSUam0CFx9DS3tqLdxn+Xk=; b=j2B9PQwEXWmO+rrRvy56fAtJihg7fJndDROBBV0xj9nWo1vrLU0EL1HPK6gJ3Is2JD U9HpDZGAyNx5aqrMc+bk2PPGLuLFAMfg12aQg9qi2Hu54xcUuQDk00wtkVJ0npbCY3JT MGvmy8vLFtbEQz5+n1obswxXCUNgkluNrfpWhFHSTHJxojrIwCu/AOxMsmNmOGcv7TjJ TIQX80VNHUmiILrzP0xzSGOzy095gk5oPn/6yVx8JDFtY2UtUjMUJN/Z1F1zdE18/Ngw 4yH3ItSWLdSFamrTl/LyxLptDswa1g6SmNvBUE6l6k2QgvtFtS12qmcVoJgU1FMRo6xX 6ZmA== X-Gm-Message-State: AOAM530ZYprbcQUg6gJL5+RUncXrnKLFVJpWkWNZFjAyObIfr72VlRSF L3+H8GOWzKfDHg2CAQcFksdUdg== X-Google-Smtp-Source: ABdhPJxEslujd3tp9T1ofdE6n0YODMisS2U8S0qulVyj48Ul/uxdH4vlyBD4bOXB2UljyUZYhZqVDA== X-Received: by 2002:aa7:93a2:0:b029:142:2501:39f4 with SMTP id x2-20020aa793a20000b0290142250139f4mr838077pff.67.1601077666482; Fri, 25 Sep 2020 16:47:46 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id q5sm3603706pfb.184.2020.09.25.16.47.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Sep 2020 16:47:45 -0700 (PDT) Date: Fri, 25 Sep 2020 16:47:44 -0700 From: Kees Cook To: Ard Biesheuvel Subject: Re: KASLR support on ARM with Kernel 4.9 and 4.14 Message-ID: <202009251647.FD8CECD4@keescook> References: <202009251301.A1FD183582@keescook> <202009251338.D17FB071@keescook> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Cc: Mark Rutland , Thomas Garnier , Pintu Agarwal , Arnd Bergmann , Ard Biesheuvel , Marc Zyngier , Kernelnewbies , Russell King - ARM Linux , open list , Tony Lindgren , nico@linaro.org, Dave Martin , matt@codeblueprint.co.uk, "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" X-BeenThere: kernelnewbies@kernelnewbies.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Learn about the Linux kernel List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kernelnewbies-bounces+kernelnewbies=archiver.kernel.org@kernelnewbies.org On Fri, Sep 25, 2020 at 11:09:10PM +0200, Ard Biesheuvel wrote: > On Fri, 25 Sep 2020 at 22:47, Kees Cook wrote: > > > > 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). > > > > Ah yes, good point. But it does look suspiciously like they are being > mangled in a similar way. > > For a 3/1 split ARM kernel of the typical size, all kernel virtual > addresses start with 0xc0, and given that the kernel is located at the > start of the linear map, those addresses cannot change even if you > move the kernel around in physical memory. I wonder if this is an Android Common kernel? I think there was %p hashing in there before v4.15, but with a different implementation... -- Kees Cook _______________________________________________ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies