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,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 CF6DCC433E2 for ; Wed, 15 Jul 2020 08:52:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A29BB20672 for ; Wed, 15 Jul 2020 08:52:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="hHzdxBJ1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730460AbgGOIwd (ORCPT ); Wed, 15 Jul 2020 04:52:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55882 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730445AbgGOIwc (ORCPT ); Wed, 15 Jul 2020 04:52:32 -0400 Received: from mail-io1-xd43.google.com (mail-io1-xd43.google.com [IPv6:2607:f8b0:4864:20::d43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C63CAC061755 for ; Wed, 15 Jul 2020 01:52:32 -0700 (PDT) Received: by mail-io1-xd43.google.com with SMTP id e64so1388157iof.12 for ; Wed, 15 Jul 2020 01:52:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:reply-to:from:date:message-id :subject:to:cc; bh=3Z4IpLUKocM3OEmb2Wb4pmzCIIom6GoJeorw5OSNFmA=; b=hHzdxBJ1OQGEfhC90QrC2rcV6mefC3VdSTniGM9hIQKPOR8JXTj7WKNBfXh153QO+z sFiPrRzfbR5yOnd870qHFxRdAdEYgeagfwrYPFcUmAFA+3yJg2yqc2O9iNUOGWqhZ/7W /+RTXMs+zfL+gFZvJLzBprAPHqA+v3Q8eFvUatZCmcRlNjRcjfy7vI6FNIn+nRL+ueS1 FGA4P96247zfhiVYwY56WyXY5HoY9wvxCmqjOeslQ0oK8cmR4QPsVKVdc3Tq60C81odk AFuDLyzF/3vXymk+0OE7K/W//GsO2IRZ/m4z3pmbYQUVY67PaLiWpFhncFKvbwP6oySe yEJg== 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:reply-to :from:date:message-id:subject:to:cc; bh=3Z4IpLUKocM3OEmb2Wb4pmzCIIom6GoJeorw5OSNFmA=; b=O7jLNp8orujJgAY6Gv8Ww06s8UoXWmmx6ZkZpTDa27kC6VWefoavbXfOBZeUtlCUZR qIFTenCGaj0KnDVUQbmc/aLG6IM3jd2M2W0bpbiL6o7FIViNQHuESUZDX7D1pWRWl+hg oT/MWF+W0ZqyyUCkNtJrPnOVnA+eLptNf7QPL+jaXqvuwQ4cFUuvq0fDCcY6OMcFq396 ibJd+iJT8yNlNUXDTU2DmHhUApJpy+3YmtDok4Jl+hZVNfp9fFdqfIm2ZZ56VYmD3O6d hkbipDjwfCI6nhGqbqqyXS2IivOYg7Gc4p7zwhXT2z2RBn6VZ6WSiv7S+koaHfXOjJIv 2G9A== X-Gm-Message-State: AOAM5304XgtC0eHoYcnyd+woMeZETT+LPXUEZuyKUesnzgs6ziI3Gd29 KHS9djyfWttqV8Rwtmt3ETopBG495C7Ef7sUSbU= X-Google-Smtp-Source: ABdhPJyp2Jkk8UtUIOJ+t1y4YAmr65LCFaVZo0jz/FKxkcsalM41AmdbHnW8iXebFlCIFGEZZO1+cf9JYfZpLRExKNU= X-Received: by 2002:a02:ce9a:: with SMTP id y26mr10812220jaq.121.1594803152177; Wed, 15 Jul 2020 01:52:32 -0700 (PDT) MIME-Version: 1.0 References: <20200714023836.2310569-1-nivedita@alum.mit.edu> <20200715004133.1430068-2-nivedita@alum.mit.edu> In-Reply-To: <20200715004133.1430068-2-nivedita@alum.mit.edu> Reply-To: sedat.dilek@gmail.com From: Sedat Dilek Date: Wed, 15 Jul 2020 10:52:20 +0200 Message-ID: Subject: Re: [PATCH v5 1/7] x86/boot/compressed: Move .got.plt entries out of the .got section To: Arvind Sankar Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, Nick Desaulniers , Fangrui Song , Dmitry Golovin , Clang-Built-Linux ML , Ard Biesheuvel , Masahiro Yamada , Daniel Kiper , Kees Cook , Nathan Chancellor , Arnd Bergmann , "H . J . Lu" , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 15, 2020 at 2:41 AM Arvind Sankar wrote: > > From: Ard Biesheuvel > > The .got.plt section contains the part of the GOT which is used by PLT > entries, and which gets updated lazily by the dynamic loader when > function calls are dispatched through those PLT entries. > > On fully linked binaries such as the kernel proper or the decompressor, > this never happens, and so in practice, the .got.plt section consists > only of the first 3 magic entries that are meant to point at the _DYNAMIC > section and at the fixup routine in the loader. However, since we don't > use a dynamic loader, those entries are never populated or used. > > This means that treating those entries like ordinary GOT entries, and > updating their values based on the actual placement of the executable in > memory is completely pointless, and we can just ignore the .got.plt > section entirely, provided that it has no additional entries beyond > the first 3 ones. > > So add an assertion in the linker script to ensure that this assumption > holds, and move the contents out of the [_got, _egot) memory range that > is modified by the GOT fixup routines. > > While at it, drop the KEEP(), since it has no effect on the contents > of output sections that are created by the linker itself. > > Reviewed-by: Kees Cook > Signed-off-by: Ard Biesheuvel > Acked-by: Arvind Sankar > Signed-off-by: Arvind Sankar > From: Ard Biesheuvel > Link: https://lore.kernel.org/r/20200523120021.34996-2-ardb@kernel.org Tested-by: Sedat Dilek - Sedat - > --- > arch/x86/boot/compressed/vmlinux.lds.S | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S > index 8f1025d1f681..b17d218ccdf9 100644 > --- a/arch/x86/boot/compressed/vmlinux.lds.S > +++ b/arch/x86/boot/compressed/vmlinux.lds.S > @@ -44,10 +44,13 @@ SECTIONS > } > .got : { > _got = .; > - KEEP(*(.got.plt)) > KEEP(*(.got)) > _egot = .; > } > + .got.plt : { > + *(.got.plt) > + } > + > .data : { > _data = . ; > *(.data) > @@ -77,3 +80,9 @@ SECTIONS > > DISCARDS > } > + > +#ifdef CONFIG_X86_64 > +ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT entries detected!") > +#else > +ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!") > +#endif > -- > 2.26.2 >