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=-11.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SIGNED_OFF_BY,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 E5AAEC5517A for ; Mon, 26 Oct 2020 17:53:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 909E322265 for ; Mon, 26 Oct 2020 17:53:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1781412AbgJZRxP (ORCPT ); Mon, 26 Oct 2020 13:53:15 -0400 Received: from mail-ot1-f66.google.com ([209.85.210.66]:34705 "EHLO mail-ot1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1781399AbgJZRxP (ORCPT ); Mon, 26 Oct 2020 13:53:15 -0400 Received: by mail-ot1-f66.google.com with SMTP id k3so8214056otp.1; Mon, 26 Oct 2020 10:53:14 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=aSP7w6hGOtdU2uA5tvPlkM6OwSpoT9pVdwMoOdt+1fQ=; b=Cv+rJF6Y4NZozdmD79G0UFQ60mhIHnJF0O4c0Gd7Jj6j+JEWuL4KtrydHy0foChe6o csZItIZpCP19LoNHVzX9sszguH31MGDTBZgBHNKITG4V5QwyzV1xv8EJqHpUJKSmdUiV KWgZJSdjzX6lERZ1j421wHnYePNW/chWC4a4yKUC2MGTlfV9vjrWTFHEjhoiuGLcjjnL 1hlqz1XDQWuOWfe1fe9bX+zVzCKh1DdOpw0rrcItcVH45XpwzcSFfubXXk67S2k8K0VP EMbSnzc5TF8BxGS1381+l7Zfq7HkGPSF9gBIz8KNSeNZq/mPyleoGslPUVsAFQ+HTQXU T/pA== X-Gm-Message-State: AOAM5328KH5k6U0t5G2xX1pfiVmbWUWJEfkEnxHOTFC9yqfv9xgc4sbV ZUOfxT3ow+s7nl4v9ffEXLeWKez2yxG8GPendlw= X-Google-Smtp-Source: ABdhPJzyLS3lSQG+HGr+V6jPcJm2j+7DqH4t1c+0Dyl/dUwUJFnTsFRRuWj5SDZDmDC54eq2tej3wmmsezKdR5Pt/uo= X-Received: by 2002:a05:6830:210a:: with SMTP id i10mr14302905otc.145.1603734793886; Mon, 26 Oct 2020 10:53:13 -0700 (PDT) MIME-Version: 1.0 References: <20200821194310.3089815-1-keescook@chromium.org> <20200821194310.3089815-14-keescook@chromium.org> In-Reply-To: From: Geert Uytterhoeven Date: Mon, 26 Oct 2020 18:53:02 +0100 Message-ID: Subject: Re: [PATCH v6 13/29] arm64/build: Assert for unwanted sections To: Nick Desaulniers Cc: Ard Biesheuvel , Kees Cook , Ingo Molnar , Catalin Marinas , Mark Rutland , Peter Collingbourne , James Morse , Borislav Petkov , Ingo Molnar , Russell King , Masahiro Yamada , Arvind Sankar , Nathan Chancellor , Arnd Bergmann , "the arch/x86 maintainers" , clang-built-linux , Linux-Arch , linux-efi , Linux ARM , Linux Kernel Mailing List , Linux-Renesas Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org Hi Nick, On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers wrote: > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > wrote: > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel wrote: > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven wrote: > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven wrote: > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven wrote: > > > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook wrote: > > > > > > > In preparation for warning on orphan sections, discard > > > > > > > unwanted non-zero-sized generated sections, and enforce other > > > > > > > expected-to-be-zero-sized sections (since discarding them might hide > > > > > > > problems with them suddenly gaining unexpected entries). > > > > > > > > > > > > > > Suggested-by: Ard Biesheuvel > > > > > > > Signed-off-by: Kees Cook > > > > > > > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > > > > > sections") in v5.10-rc1, and is causing the following error with > > > > > > renesas_defconfig[1]: > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > > > > > > > > > I bisected the error to the aforementioned commit, but understand this > > > > > > is not the real reason. If I revert this commit, I still get: > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > placement"), which is another red herring. > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > causing the warning. > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > missing from someone's KBUILD_CFLAGS. > But I don't see anything curious in kernel/bpf/Makefile, unless > cc-disable-warning is somehow broken. Yeah, I noticed it's added in arch/arm64/Makefile, and verified that it is actually passed when building kernel/bpf/core.o. > > > > > If I compile core.c with "-g" added, like arm64 defconfig does, the > > > > > eh_frame section is no longer emitted. > > > > > > > > > > Hence setting CONFIG_DEBUG_INFO=y, cfr. arm64 defconfig, the warning > > > > > is gone, but I'm back to the the "Unexpected GOT/PLT entries" below... > > > > > > > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > > > the problem). > > > > > > > > Reverting both > > > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > > > seems to solve my problems, without any ill effects? > > > > > > > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > > > > > The presence of .data.rel.ro and .got.plt sections suggests that the > > > toolchain is using -fpie and/or -z relro to build shared objects > > > rather than a fully linked bare metal binary. > > > > > > Which toolchain are you using? Does adding -fno-pie to the compiler > > > > gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04) from Ubuntu 20.04LTS. > > > > > command line and/or adding -z norelro to the linker command line make > > > any difference? > > > > I'll give that a try later... > > This patch just got picked up into the for-next branch of the arm64 > tree; it enables `-z norelro` regardless of configs. > https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?h=for-next/core&id=3b92fa7485eba16b05166fddf38ab42f2ff6ab95 > If you apply that, that should help you test `-z norelro` quickly. Thanks, will give that a try, too. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds