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=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 B9619C433E3 for ; Fri, 17 Jul 2020 20:18:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A1A9920704 for ; Fri, 17 Jul 2020 20:18:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728817AbgGQUSG (ORCPT ); Fri, 17 Jul 2020 16:18:06 -0400 Received: from mail-qt1-f195.google.com ([209.85.160.195]:36536 "EHLO mail-qt1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728238AbgGQUSF (ORCPT ); Fri, 17 Jul 2020 16:18:05 -0400 Received: by mail-qt1-f195.google.com with SMTP id x62so8617721qtd.3 for ; Fri, 17 Jul 2020 13:18:04 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=RhWnzCqvgTN++G31OGgg9qNDvvhiuki5nvpw8uOP67s=; b=r8Wabn2ZX944rGIMiiIGizL3JBQrMeaQiop98IQlP8n+ODWrZV6s073QThV3Up/PLl q5RRCp1VM1MjW68KO7CLbVNjbRU175d8tn6ULr+B+BFOm3CKcVYTWwq0tpJ20csDErxV TJlOWRbC7nbqghMf/vkJzN8iNecsCJVBDT8BcLG1Vp16UWC1/JAGMhtEYMlceOjKWwsI +3aF0MgAyF+9hZEAHtn6bOT9P3ZW8s50S1lLW3eEYCyV+WRT49sr3EhB93/vFMO91iM0 u5yx6XJ9FpKr7i/jECBHlx0rGNoju6FZ/NFcdbR0LduHFb7uZTOaQbRzKdwLPVyFsgMi Xrrg== X-Gm-Message-State: AOAM5308R7+J8KrdD/E6sRSyK5uiJ/TcB7FygIaYn/wUp/HyNbMXNcqF 3sV1A1aEO7NUweV6ViD2PXQ= X-Google-Smtp-Source: ABdhPJyENdon7efSSSBH9gQJ2IKuy+6zwZMCEaRN2dhPljIOqIAdiDrGBSLEAzua+/swLDkG0G7TqA== X-Received: by 2002:ac8:4e4f:: with SMTP id e15mr12433072qtw.347.1595017084364; Fri, 17 Jul 2020 13:18:04 -0700 (PDT) Received: from rani.riverdale.lan ([2001:470:1f07:5f3::b55f]) by smtp.gmail.com with ESMTPSA id a28sm9509977qko.45.2020.07.17.13.18.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Jul 2020 13:18:03 -0700 (PDT) From: Arvind Sankar To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org Cc: Nick Desaulniers , Fangrui Song , Dmitry Golovin , clang-built-linux@googlegroups.com, Ard Biesheuvel , Masahiro Yamada , Sedat Dilek , Kees Cook , Nathan Chancellor , Arnd Bergmann , "H . J . Lu" , linux-kernel@vger.kernel.org Subject: [PATCH-next v5 1/7] x86/boot/compressed: Move .got.plt entries out of the .got section Date: Fri, 17 Jul 2020 16:17:55 -0400 Message-Id: <20200717201801.3661843-2-nivedita@alum.mit.edu> X-Mailer: git-send-email 2.26.2 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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