From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kees Cook Subject: Re: [PATCH 07/29] x86: Restore "text" Program Header with dummy section Date: Thu, 10 Oct 2019 09:46:36 -0700 Message-ID: <201910100944.92CFB97157@keescook> References: <20190926175602.33098-1-keescook@chromium.org> <20190926175602.33098-8-keescook@chromium.org> <20191010103305.GD7658@zn.tnic> Mime-Version: 1.0 Return-path: 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=ucc2HcE1KFej2LH6JBkm0K2H0dlib4/rpE4E9DkdWnQ=; b=jCH7hVEz9DolIZ1tWTZ2WBzCCWqtC/N1Zw7aqh/YsT1JbgkR+jdLg1c8HFybVnrnDt zDT8Pac3++Knf0BDJnT4AHK6EvCPW0ovTGp9VFWoRwYqDitcprYMafhTNkb/D4GuI+mu p5DqysPLL8vgpaaxV3VItm4rQa6UKBD0JpAMw= Content-Disposition: inline In-Reply-To: <20191010103305.GD7658@zn.tnic> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Borislav Petkov Cc: Thomas Gleixner , Rick Edgecombe , Ingo Molnar , "H. Peter Anvin" , Dave Hansen , Andy Lutomirski , Arnd Bergmann , linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-c6x-dev@linux-c6x.org, Yoshinori Sato , Michal Simek , linux-parisc@vger.kernel.org, linux-xtensa@linux-xtensa.org, x86@kernel.org, linux-kernel@vger.kernel.org On Thu, Oct 10, 2019 at 12:33:05PM +0200, Borislav Petkov wrote: > On Thu, Sep 26, 2019 at 10:55:40AM -0700, Kees Cook wrote: > > Instead of depending on markings in the section following NOTES to > > restore the associated Program Header, use a dummy section, as done > > in other architectures. > > This is very laconic and after some staring at ld.info, I think you mean > this: > > " If you place a section in one or more segments using ':PHDR', then > the linker will place all subsequent allocatable sections which do not > specify ':PHDR' in the same segments." > > but I could be way off. Yes, no? > > IOW, please write in the commit messages first what the problem is > you're addressing. Yeah, that's much improved. I really struggled to describe this, given how weird the linker script logic is here. > > --- a/arch/x86/kernel/vmlinux.lds.S > > +++ b/arch/x86/kernel/vmlinux.lds.S > > @@ -147,8 +147,9 @@ SECTIONS > > } :text = 0x9090 > > > > NOTES :text :note > > + .dummy : { *(.dummy) } :text > > > > - EXCEPTION_TABLE(16) :text = 0x9090 > > + EXCEPTION_TABLE(16) > > This is killing the filler byte but I have a suspicion that'll change > eventually to INT3... :) Yes, though since the exception table isn't executable, filling with 0x90 has no meaning, and I think when I looked at the alignment there were actually no fill bytes from here on. But it doesn't matter; it all goes away in the end. -- Kees Cook From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kees Cook Date: Thu, 10 Oct 2019 16:46:36 +0000 Subject: Re: [PATCH 07/29] x86: Restore "text" Program Header with dummy section Message-Id: <201910100944.92CFB97157@keescook> List-Id: References: <20190926175602.33098-1-keescook@chromium.org> <20190926175602.33098-8-keescook@chromium.org> <20191010103305.GD7658@zn.tnic> In-Reply-To: <20191010103305.GD7658@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Borislav Petkov Cc: Thomas Gleixner , Rick Edgecombe , Ingo Molnar , "H. Peter Anvin" , Dave Hansen , Andy Lutomirski , Arnd Bergmann , linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-c6x-dev@linux-c6x.org, Yoshinori Sato , Michal Simek , linux-parisc@vger.kernel.org, linux-xtensa@linux-xtensa.org, x86@kernel.org, linux-kernel@vger.kernel.org On Thu, Oct 10, 2019 at 12:33:05PM +0200, Borislav Petkov wrote: > On Thu, Sep 26, 2019 at 10:55:40AM -0700, Kees Cook wrote: > > Instead of depending on markings in the section following NOTES to > > restore the associated Program Header, use a dummy section, as done > > in other architectures. > > This is very laconic and after some staring at ld.info, I think you mean > this: > > " If you place a section in one or more segments using ':PHDR', then > the linker will place all subsequent allocatable sections which do not > specify ':PHDR' in the same segments." > > but I could be way off. Yes, no? > > IOW, please write in the commit messages first what the problem is > you're addressing. Yeah, that's much improved. I really struggled to describe this, given how weird the linker script logic is here. > > --- a/arch/x86/kernel/vmlinux.lds.S > > +++ b/arch/x86/kernel/vmlinux.lds.S > > @@ -147,8 +147,9 @@ SECTIONS > > } :text = 0x9090 > > > > NOTES :text :note > > + .dummy : { *(.dummy) } :text > > > > - EXCEPTION_TABLE(16) :text = 0x9090 > > + EXCEPTION_TABLE(16) > > This is killing the filler byte but I have a suspicion that'll change > eventually to INT3... :) Yes, though since the exception table isn't executable, filling with 0x90 has no meaning, and I think when I looked at the alignment there were actually no fill bytes from here on. But it doesn't matter; it all goes away in the end. -- Kees Cook 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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 360CCC4360C for ; Thu, 10 Oct 2019 16:48:59 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 8ABF32190F for ; Thu, 10 Oct 2019 16:48:58 +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="jCH7hVEz" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8ABF32190F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 46pxqp53VSzDqQs for ; Fri, 11 Oct 2019 03:48:54 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=chromium.org (client-ip=2607:f8b0:4864:20::443; helo=mail-pf1-x443.google.com; envelope-from=keescook@chromium.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=chromium.org Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=chromium.org header.i=@chromium.org header.b="jCH7hVEz"; dkim-atps=neutral Received: from mail-pf1-x443.google.com (mail-pf1-x443.google.com [IPv6:2607:f8b0:4864:20::443]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 46pxnG5txszDqPQ for ; Fri, 11 Oct 2019 03:46:40 +1100 (AEDT) Received: by mail-pf1-x443.google.com with SMTP id 205so4279693pfw.2 for ; Thu, 10 Oct 2019 09:46:40 -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=ucc2HcE1KFej2LH6JBkm0K2H0dlib4/rpE4E9DkdWnQ=; b=jCH7hVEz9DolIZ1tWTZ2WBzCCWqtC/N1Zw7aqh/YsT1JbgkR+jdLg1c8HFybVnrnDt zDT8Pac3++Knf0BDJnT4AHK6EvCPW0ovTGp9VFWoRwYqDitcprYMafhTNkb/D4GuI+mu p5DqysPLL8vgpaaxV3VItm4rQa6UKBD0JpAMw= 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=ucc2HcE1KFej2LH6JBkm0K2H0dlib4/rpE4E9DkdWnQ=; b=qa95JCyreczQm/EMq/ptYb2lZm18fxdyDFTq6LO+SyEzaQVNQW2aIxOhaprxasjqgq B4zLBtCF4Rnfx9NhEuvpDm9poQVYWnx9gxOmLctZGZt8rm68jTjYWwXpDLMBKIzVdjUP 6+eWIAEb1+7hS4mUZ8P6fO0aDSDK8BanK0YRsYb0miWaDuxW4MvGniJF5ext+NaKqSih 233j5+o0bp9l3rs8+hZn1+tSEj9Dpj8dRPpiSFrf/znJDokofAVa67i5PzflNb1FtagT a03YAImwiIwI05ETWKw14KGfuVuSDzeboPB1IJZQtR+s8k0Sfh8/KFKXP9H6n2+CszZk CZKg== X-Gm-Message-State: APjAAAUrOwvfecjYZcqVQUDQqtk1zkwXRJGGLF033fS5Ax6DJPXWzmGF UG7glvhHUVVuIxgJe/eInRjk2g== X-Google-Smtp-Source: APXvYqz81XDUB+KawYO30nxn2eoCx5FdYR8TngYKUPz81EWriv3MgYEwn6iW+aXgb9GpyhSssUlr1A== X-Received: by 2002:a63:e1f:: with SMTP id d31mr11802284pgl.379.1570725998193; Thu, 10 Oct 2019 09:46:38 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id k5sm4896915pgo.45.2019.10.10.09.46.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Oct 2019 09:46:37 -0700 (PDT) Date: Thu, 10 Oct 2019 09:46:36 -0700 From: Kees Cook To: Borislav Petkov Subject: Re: [PATCH 07/29] x86: Restore "text" Program Header with dummy section Message-ID: <201910100944.92CFB97157@keescook> References: <20190926175602.33098-1-keescook@chromium.org> <20190926175602.33098-8-keescook@chromium.org> <20191010103305.GD7658@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191010103305.GD7658@zn.tnic> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Michal Simek , linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-c6x-dev@linux-c6x.org, Arnd Bergmann , linux-xtensa@linux-xtensa.org, linux-kernel@vger.kernel.org, Dave Hansen , x86@kernel.org, Yoshinori Sato , Ingo Molnar , linux-parisc@vger.kernel.org, Andy Lutomirski , "H. Peter Anvin" , Thomas Gleixner , Rick Edgecombe , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Oct 10, 2019 at 12:33:05PM +0200, Borislav Petkov wrote: > On Thu, Sep 26, 2019 at 10:55:40AM -0700, Kees Cook wrote: > > Instead of depending on markings in the section following NOTES to > > restore the associated Program Header, use a dummy section, as done > > in other architectures. > > This is very laconic and after some staring at ld.info, I think you mean > this: > > " If you place a section in one or more segments using ':PHDR', then > the linker will place all subsequent allocatable sections which do not > specify ':PHDR' in the same segments." > > but I could be way off. Yes, no? > > IOW, please write in the commit messages first what the problem is > you're addressing. Yeah, that's much improved. I really struggled to describe this, given how weird the linker script logic is here. > > --- a/arch/x86/kernel/vmlinux.lds.S > > +++ b/arch/x86/kernel/vmlinux.lds.S > > @@ -147,8 +147,9 @@ SECTIONS > > } :text = 0x9090 > > > > NOTES :text :note > > + .dummy : { *(.dummy) } :text > > > > - EXCEPTION_TABLE(16) :text = 0x9090 > > + EXCEPTION_TABLE(16) > > This is killing the filler byte but I have a suspicion that'll change > eventually to INT3... :) Yes, though since the exception table isn't executable, filling with 0x90 has no meaning, and I think when I looked at the alignment there were actually no fill bytes from here on. But it doesn't matter; it all goes away in the end. -- Kees Cook